diff --git a/mod/fbrowser.php b/mod/fbrowser.php
index 81284d6b9..60b290850 100644
--- a/mod/fbrowser.php
+++ b/mod/fbrowser.php
@@ -47,7 +47,7 @@ function fbrowser_content(App $a)
 	}
 
 	// Needed to match the correct template in a module that uses a different theme than the user/site/default
-	$theme = Strings::sanitizeFilePathItem($_GET['theme'] ?? null);
+	$theme = Strings::sanitizeFilePathItem($_GET['theme'] ?? '');
 	if ($theme && is_file("view/theme/$theme/config.php")) {
 		$a->setCurrentTheme($theme);
 	}
diff --git a/mod/photos.php b/mod/photos.php
index 0e2299770..977cebf20 100644
--- a/mod/photos.php
+++ b/mod/photos.php
@@ -187,7 +187,7 @@ function photos_post(App $a)
 	}
 
 	if (DI::args()->getArgc() > 3 && DI::args()->getArgv()[2] === 'album') {
-		if (!Strings::isHex(DI::args()->getArgv()[3])) {
+		if (!Strings::isHex(DI::args()->getArgv()[3] ?? '')) {
 			DI::baseUrl()->redirect('photos/' . $user['nickname'] . '/album');
 		}
 		$album = hex2bin(DI::args()->getArgv()[3]);
@@ -892,7 +892,7 @@ function photos_content(App $a)
 			return;
 		}
 
-		$selname = Strings::isHex($datum) ? hex2bin($datum) : '';
+		$selname = (!is_null($datum) && Strings::isHex($datum)) ? hex2bin($datum) : '';
 
 		$albumselect = '';
 
@@ -954,7 +954,7 @@ function photos_content(App $a)
 	// Display a single photo album
 	if ($datatype === 'album') {
 		// if $datum is not a valid hex, redirect to the default page
-		if (!Strings::isHex($datum)) {
+		if (is_null($datum) || !Strings::isHex($datum)) {
 			DI::baseUrl()->redirect('photos/' . $user['nickname']. '/album');
 		}
 		$album = hex2bin($datum);
diff --git a/src/Console/Addon.php b/src/Console/Addon.php
index 1389e97bf..74b081810 100644
--- a/src/Console/Addon.php
+++ b/src/Console/Addon.php
@@ -116,8 +116,7 @@ HELP;
 	/**
 	 * Lists plugins
 	 *
-	 * @return int Return code of this command
-	 *
+	 * @return int|bool Return code of this command, false on error (?)
 	 * @throws \Exception
 	 */
 	private function list()
@@ -165,10 +164,9 @@ HELP;
 	 * Enables an addon
 	 *
 	 * @return int Return code of this command
-	 *
 	 * @throws \Exception
 	 */
-	private function enable()
+	private function enable(): int
 	{
 		$addonname = $this->getArgument(1);
 
@@ -190,10 +188,9 @@ HELP;
 	 * Disables an addon
 	 *
 	 * @return int Return code of this command
-	 *
 	 * @throws \Exception
 	 */
-	private function disable()
+	private function disable(): int
 	{
 		$addonname = $this->getArgument(1);
 
diff --git a/src/Core/Addon.php b/src/Core/Addon.php
index f6d0d4974..37ef335a4 100644
--- a/src/Core/Addon.php
+++ b/src/Core/Addon.php
@@ -124,7 +124,7 @@ class Addon
 	 * @return void
 	 * @throws \Exception
 	 */
-	public static function uninstall($addon)
+	public static function uninstall(string $addon)
 	{
 		$addon = Strings::sanitizeFilePathItem($addon);
 
@@ -149,7 +149,7 @@ class Addon
 	 * @return bool
 	 * @throws \Exception
 	 */
-	public static function install($addon)
+	public static function install(string $addon): bool
 	{
 		$addon = Strings::sanitizeFilePathItem($addon);
 
@@ -185,6 +185,8 @@ class Addon
 
 	/**
 	 * reload all updated addons
+	 *
+	 * @return void
 	 */
 	public static function reload()
 	{
@@ -222,7 +224,7 @@ class Addon
 	 * @return array with the addon information
 	 * @throws \Exception
 	 */
-	public static function getInfo($addon)
+	public static function getInfo(string $addon): array
 	{
 		$addon = Strings::sanitizeFilePathItem($addon);
 
@@ -287,7 +289,7 @@ class Addon
 	 * @param string $addon
 	 * @return boolean
 	 */
-	public static function isEnabled($addon)
+	public static function isEnabled(string $addon): bool
 	{
 		return in_array($addon, self::$addons);
 	}
@@ -297,7 +299,7 @@ class Addon
 	 *
 	 * @return array
 	 */
-	public static function getEnabledList()
+	public static function getEnabledList(): array
 	{
 		return self::$addons;
 	}
@@ -308,7 +310,7 @@ class Addon
 	 * @return array
 	 * @throws \Exception
 	 */
-	public static function getVisibleList()
+	public static function getVisibleList(): array
 	{
 		$visible_addons = [];
 		$stmt = DBA::select('addon', ['name'], ['hidden' => false, 'installed' => true]);
diff --git a/src/Core/Hook.php b/src/Core/Hook.php
index 89e882e35..f2fb52f5e 100644
--- a/src/Core/Hook.php
+++ b/src/Core/Hook.php
@@ -49,6 +49,8 @@ class Hook
 
 	/**
 	 * Load hooks
+	 *
+	 * @return void
 	 */
 	public static function loadHooks()
 	{
@@ -69,8 +71,9 @@ class Hook
 	 * @param string $hook
 	 * @param string $file
 	 * @param string $function
+	 * @return void
 	 */
-	public static function add($hook, $file, $function)
+	public static function add(string $hook, string $file, string $function)
 	{
 		if (!array_key_exists($hook, self::$hooks)) {
 			self::$hooks[$hook] = [];
@@ -90,7 +93,7 @@ class Hook
 	 * @return mixed|bool
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function register($hook, $file, $function, $priority = 0)
+	public static function register(string $hook, string $file, string $function, int $priority = 0)
 	{
 		$file = str_replace(DI::app()->getBasePath() . DIRECTORY_SEPARATOR, '', $file);
 
@@ -111,7 +114,7 @@ class Hook
 	 * @return boolean
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function unregister($hook, $file, $function)
+	public static function unregister(string $hook, string $file, string $function): bool
 	{
 		$relative_file = str_replace(DI::app()->getBasePath() . DIRECTORY_SEPARATOR, '', $file);
 
@@ -120,8 +123,8 @@ class Hook
 		self::delete($condition);
 
 		$condition = ['hook' => $hook, 'file' => $relative_file, 'function' => $function];
-		$result = self::delete($condition);
-		return $result;
+
+		return self::delete($condition);
 	}
 
 	/**
@@ -130,7 +133,7 @@ class Hook
 	 * @param  string $name Name of the hook
 	 * @return array
 	 */
-	public static function getByName($name)
+	public static function getByName(string $name): array
 	{
 		$return = [];
 
@@ -149,9 +152,10 @@ class Hook
 	 * @param integer $priority of the hook
 	 * @param string  $name     of the hook to call
 	 * @param mixed   $data     to transmit to the callback handler
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function fork($priority, $name, $data = null)
+	public static function fork(int $priority, string $name, $data = null)
 	{
 		if (array_key_exists($name, self::$hooks)) {
 			foreach (self::$hooks[$name] as $hook) {
@@ -184,9 +188,10 @@ class Hook
 	 *
 	 * @param string        $name of the hook to call
 	 * @param string|array &$data to transmit to the callback handler
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function callAll($name, &$data = null)
+	public static function callAll(string $name, &$data = null)
 	{
 		if (array_key_exists($name, self::$hooks)) {
 			foreach (self::$hooks[$name] as $hook) {
@@ -202,9 +207,10 @@ class Hook
 	 * @param string          $name of the hook to call
 	 * @param array           $hook Hook data
 	 * @param string|array   &$data to transmit to the callback handler
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function callSingle(App $a, $name, $hook, &$data = null)
+	public static function callSingle(App $a, string $name, array $hook, &$data = null)
 	{
 		// Don't run a theme's hook if the user isn't using the theme
 		if (strpos($hook[0], 'view/theme/') !== false && strpos($hook[0], 'view/theme/' . $a->getCurrentTheme()) === false) {
@@ -229,7 +235,7 @@ class Hook
 	 * @param string $name Name of the addon
 	 * @return boolean
 	 */
-	public static function isAddonApp($name)
+	public static function isAddonApp(string $name): bool
 	{
 		$name = Strings::sanitizeFilePathItem($name);
 
@@ -253,7 +259,7 @@ class Hook
 	 * @return bool
 	 * @throws \Exception
 	 */
-	public static function delete(array $condition)
+	public static function delete(array $condition): bool
 	{
 		$result = DBA::delete('hook', $condition);
 
@@ -273,7 +279,7 @@ class Hook
 	 * @return bool
 	 * @throws \Exception
 	 */
-	private static function insert(array $condition)
+	private static function insert(array $condition): bool
 	{
 		$result = DBA::insert('hook', $condition);
 
diff --git a/src/Core/L10n.php b/src/Core/L10n.php
index 050c19073..2c45fb955 100644
--- a/src/Core/L10n.php
+++ b/src/Core/L10n.php
@@ -128,7 +128,7 @@ class L10n
 	private function setLangFromSession(IHandleSessions $session)
 	{
 		if ($session->get('language') !== $this->lang) {
-			$this->loadTranslationTable($session->get('language'));
+			$this->loadTranslationTable($session->get('language') ?? $this->lang);
 		}
 	}
 
@@ -140,10 +140,10 @@ class L10n
 	 * Uses an App object shim since all the strings files refer to $a->strings
 	 *
 	 * @param string $lang language code to load
-	 *
+	 * @return void
 	 * @throws \Exception
 	 */
-	private function loadTranslationTable($lang)
+	private function loadTranslationTable(string $lang)
 	{
 		$lang = Strings::sanitizeFilePathItem($lang);
 
@@ -183,7 +183,7 @@ class L10n
 	 *
 	 * @return string The two-letter language code
 	 */
-	public static function detectLanguage(array $server, array $get, string $sysLang = self::DEFAULT)
+	public static function detectLanguage(array $server, array $get, string $sysLang = self::DEFAULT): string
 	{
 		$lang_variable = $server['HTTP_ACCEPT_LANGUAGE'] ?? null;
 
@@ -269,7 +269,7 @@ class L10n
 	 *
 	 * @return string
 	 */
-	public function t($s, ...$vars)
+	public function t(string $s, ...$vars): string
 	{
 		if (empty($s)) {
 			return '';
@@ -307,7 +307,7 @@ class L10n
 	 * @return string
 	 * @throws \Exception
 	 */
-	public function tt(string $singular, string $plural, int $count)
+	public function tt(string $singular, string $plural, int $count): string
 	{
 		$s = null;
 
@@ -352,7 +352,7 @@ class L10n
 	 *
 	 * @return bool
 	 */
-	private function stringPluralSelectDefault($n)
+	private function stringPluralSelectDefault(int $n): bool
 	{
 		return $n != 1;
 	}
@@ -369,7 +369,7 @@ class L10n
 	 *
 	 * @return array
 	 */
-	public static function getAvailableLanguages()
+	public static function getAvailableLanguages(): array
 	{
 		$langs              = [];
 		$strings_file_paths = glob('view/lang/*/strings.php');
@@ -391,10 +391,9 @@ class L10n
 	 * Translate days and months names.
 	 *
 	 * @param string $s String with day or month name.
-	 *
 	 * @return string Translated string.
 	 */
-	public function getDay($s)
+	public function getDay(string $s): string
 	{
 		$ret = str_replace(['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'],
 			[$this->t('Monday'), $this->t('Tuesday'), $this->t('Wednesday'), $this->t('Thursday'), $this->t('Friday'), $this->t('Saturday'), $this->t('Sunday')],
@@ -411,10 +410,9 @@ class L10n
 	 * Translate short days and months names.
 	 *
 	 * @param string $s String with short day or month name.
-	 *
 	 * @return string Translated string.
 	 */
-	public function getDayShort($s)
+	public function getDayShort(string $s): string
 	{
 		$ret = str_replace(['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'],
 			[$this->t('Mon'), $this->t('Tue'), $this->t('Wed'), $this->t('Thu'), $this->t('Fri'), $this->t('Sat'), $this->t('Sun')],
@@ -435,7 +433,7 @@ class L10n
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @hook poke_verbs pokes array
 	 */
-	public function getPokeVerbs()
+	public function getPokeVerbs(): array
 	{
 		// index is present tense verb
 		// value is array containing past tense verb, translation of present, translation of past
@@ -461,7 +459,7 @@ class L10n
 	 * @return static A new L10n instance
 	 * @throws \Exception
 	 */
-	public function withLang(string $lang)
+	public function withLang(string $lang): L10n
 	{
 		// Don't create a new instance for same language
 		if ($lang === $this->lang) {
diff --git a/src/Core/Renderer.php b/src/Core/Renderer.php
index 29bbb2b89..879fdfe19 100644
--- a/src/Core/Renderer.php
+++ b/src/Core/Renderer.php
@@ -71,7 +71,7 @@ class Renderer
 	 * @return string
 	 * @throws ServiceUnavailableException
 	 */
-	public static function replaceMacros(string $template, array $vars = [])
+	public static function replaceMacros(string $template, array $vars = []): string
 	{
 		DI::profiler()->startRecording('rendering');
 
diff --git a/src/Core/Theme.php b/src/Core/Theme.php
index 57dfaa4d6..834787da6 100644
--- a/src/Core/Theme.php
+++ b/src/Core/Theme.php
@@ -32,7 +32,7 @@ require_once 'boot.php';
  */
 class Theme
 {
-	public static function getAllowedList()
+	public static function getAllowedList(): array
 	{
 		$allowed_themes_str = DI::config()->get('system', 'allowed_themes');
 		$allowed_themes_raw = explode(',', str_replace(' ', '', $allowed_themes_str));
@@ -69,7 +69,7 @@ class Theme
 	 * @param string $theme the name of the theme
 	 * @return array
 	 */
-	public static function getInfo($theme)
+	public static function getInfo(string $theme): array
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -133,7 +133,7 @@ class Theme
 	 * @return string
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function getScreenshot($theme)
+	public static function getScreenshot(string $theme): string
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -146,7 +146,13 @@ class Theme
 		return DI::baseUrl() . '/images/blank.png';
 	}
 
-	public static function uninstall($theme)
+	/**
+	 * Uninstalls given theme name
+	 *
+	 * @param string $theme Name of theme
+	 * @return bool true on success
+	 */
+	public static function uninstall(string $theme)
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -167,10 +173,18 @@ class Theme
 		if ($key !== false) {
 			unset($allowed_themes[$key]);
 			Theme::setAllowedList($allowed_themes);
+			return true;
 		}
+		return false;
 	}
 
-	public static function install($theme)
+	/**
+	 * Installs given theme name
+	 *
+	 * @param string $theme Name of theme
+	 * @return bool true on success
+	 */
+	public static function install(string $theme): bool
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -208,7 +222,7 @@ class Theme
 	 * @return string Path to the file or empty string if the file isn't found
 	 * @throws \Exception
 	 */
-	public static function getPathForFile($file)
+	public static function getPathForFile(string $file): string
 	{
 		$a = DI::app();
 
@@ -237,10 +251,9 @@ class Theme
 	 * Provide a sane default if nothing is chosen or the specified theme does not exist.
 	 *
 	 * @param string $theme Theme name
-	 *
 	 * @return string
 	 */
-	public static function getStylesheetPath($theme)
+	public static function getStylesheetPath(string $theme): string
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -263,10 +276,10 @@ class Theme
 	/**
 	 * Returns the path of the provided theme
 	 *
-	 * @param $theme
+	 * @param string $theme Theme name
 	 * @return string|null
 	 */
-	public static function getConfigFile($theme)
+	public static function getConfigFile(string $theme)
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
@@ -285,11 +298,11 @@ class Theme
 	/**
 	 * Returns the background color of the provided theme if available.
 	 *
-	 * @param string   $theme
+	 * @param string   $theme Theme name
 	 * @param int|null $uid   Current logged-in user id
 	 * @return string|null
 	 */
-	public static function getBackgroundColor(string $theme, $uid = null)
+	public static function getBackgroundColor(string $theme, int $uid = null)
 	{
 		$theme = Strings::sanitizeFilePathItem($theme);
 
diff --git a/src/Database/DBA.php b/src/Database/DBA.php
index d62edf6ce..e519a63cd 100644
--- a/src/Database/DBA.php
+++ b/src/Database/DBA.php
@@ -42,7 +42,7 @@ class DBA
 	 */
 	const NULL_DATETIME = '0001-01-01 00:00:00';
 
-	public static function connect()
+	public static function connect(): bool
 	{
 		return DI::dba()->connect();
 	}
@@ -58,7 +58,7 @@ class DBA
 	/**
 	 * Perform a reconnect of an existing database connection
 	 */
-	public static function reconnect()
+	public static function reconnect(): bool
 	{
 		return DI::dba()->reconnect();
 	}
@@ -90,7 +90,7 @@ class DBA
 	 *
 	 * @return string
 	 */
-	public static function serverInfo()
+	public static function serverInfo(): string
 	{
 		return DI::dba()->serverInfo();
 	}
@@ -101,7 +101,7 @@ class DBA
 	 * @return string
 	 * @throws \Exception
 	 */
-	public static function databaseName()
+	public static function databaseName(): string
 	{
 		return DI::dba()->databaseName();
 	}
@@ -112,7 +112,7 @@ class DBA
 	 * @param string $str
 	 * @return string escaped string
 	 */
-	public static function escape($str)
+	public static function escape(string $str): string
 	{
 		return DI::dba()->escape($str);
 	}
@@ -122,7 +122,7 @@ class DBA
 	 *
 	 * @return boolean is the database connected?
 	 */
-	public static function connected()
+	public static function connected(): bool
 	{
 		return DI::dba()->connected();
 	}
@@ -138,7 +138,7 @@ class DBA
 	 * @param string $sql An SQL string without the values
 	 * @return string The input SQL string modified if necessary.
 	 */
-	public static function anyValueFallback($sql)
+	public static function anyValueFallback(string $sql): string
 	{
 		return DI::dba()->anyValueFallback($sql);
 	}
@@ -152,7 +152,7 @@ class DBA
 	 * @param string $sql An SQL string without the values
 	 * @return string The input SQL string modified if necessary.
 	 */
-	public static function cleanQuery($sql)
+	public static function cleanQuery(string $sql): string
 	{
 		$search = ["\t", "\n", "\r", "  "];
 		$replace = [' ', ' ', ' ', ' '];
@@ -169,7 +169,7 @@ class DBA
 	 * @param array $args Parameter array
 	 * @return array universalized parameter array
 	 */
-	public static function getParam($args)
+	public static function getParam(array $args): array
 	{
 		unset($args[0]);
 
@@ -192,7 +192,7 @@ class DBA
 	 * @return bool|object statement object or result object
 	 * @throws \Exception
 	 */
-	public static function p($sql)
+	public static function p(string $sql)
 	{
 		$params = self::getParam(func_get_args());
 
@@ -208,8 +208,8 @@ class DBA
 	 * @return boolean Was the query successfull? False is returned only if an error occurred
 	 * @throws \Exception
 	 */
-	public static function e($sql) {
-
+	public static function e(string $sql): bool
+	{
 		$params = self::getParam(func_get_args());
 
 		return DI::dba()->e($sql, $params);
@@ -218,13 +218,12 @@ class DBA
 	/**
 	 * Check if data exists
 	 *
-	 * @param string|array $table     Table name or array [schema => table]
-	 * @param array        $condition array of fields for condition
-	 *
+	 * @param string|array $table Table name or array [schema => table]
+	 * @param array               $condition array of fields for condition
 	 * @return boolean Are there rows for that condition?
 	 * @throws \Exception
 	 */
-	public static function exists($table, $condition)
+	public static function exists($table, array $condition): bool
 	{
 		return DI::dba()->exists($table, $condition);
 	}
@@ -238,7 +237,7 @@ class DBA
 	 * @return array first row of query
 	 * @throws \Exception
 	 */
-	public static function fetchFirst($sql)
+	public static function fetchFirst(string $sql)
 	{
 		$params = self::getParam(func_get_args());
 
@@ -250,7 +249,7 @@ class DBA
 	 *
 	 * @return int Number of rows
 	 */
-	public static function affectedRows()
+	public static function affectedRows(): int
 	{
 		return DI::dba()->affectedRows();
 	}
@@ -261,7 +260,7 @@ class DBA
 	 * @param object Statement object
 	 * @return int Number of columns
 	 */
-	public static function columnCount($stmt)
+	public static function columnCount($stmt): int
 	{
 		return DI::dba()->columnCount($stmt);
 	}
@@ -271,7 +270,7 @@ class DBA
 	 * @param PDOStatement|mysqli_result|mysqli_stmt Statement object
 	 * @return int Number of rows
 	 */
-	public static function numRows($stmt)
+	public static function numRows($stmt): int
 	{
 		return DI::dba()->numRows($stmt);
 	}
@@ -297,7 +296,7 @@ class DBA
 	 * @return boolean was the insert successful?
 	 * @throws \Exception
 	 */
-	public static function insert($table, array $param, int $duplicate_mode = Database::INSERT_DEFAULT)
+	public static function insert($table, array $param, int $duplicate_mode = Database::INSERT_DEFAULT): bool
 	{
 		return DI::dba()->insert($table, $param, $duplicate_mode);
 	}
@@ -312,7 +311,7 @@ class DBA
 	 * @return boolean was the insert successful?
 	 * @throws \Exception
 	 */
-	public static function replace($table, $param)
+	public static function replace($table, array $param): bool
 	{
 		return DI::dba()->replace($table, $param);
 	}
@@ -322,7 +321,7 @@ class DBA
 	 *
 	 * @return integer Last inserted id
 	 */
-	public static function lastInsertId()
+	public static function lastInsertId(): int
 	{
 		return DI::dba()->lastInsertId();
 	}
@@ -337,7 +336,7 @@ class DBA
 	 * @return boolean was the lock successful?
 	 * @throws \Exception
 	 */
-	public static function lock($table)
+	public static function lock($table): bool
 	{
 		return DI::dba()->lock($table);
 	}
@@ -348,7 +347,7 @@ class DBA
 	 * @return boolean was the unlock successful?
 	 * @throws \Exception
 	 */
-	public static function unlock()
+	public static function unlock(): bool
 	{
 		return DI::dba()->unlock();
 	}
@@ -358,7 +357,7 @@ class DBA
 	 *
 	 * @return boolean Was the command executed successfully?
 	 */
-	public static function transaction()
+	public static function transaction(): bool
 	{
 		return DI::dba()->transaction();
 	}
@@ -368,7 +367,7 @@ class DBA
 	 *
 	 * @return boolean Was the command executed successfully?
 	 */
-	public static function commit()
+	public static function commit(): bool
 	{
 		return DI::dba()->commit();
 	}
@@ -378,7 +377,7 @@ class DBA
 	 *
 	 * @return boolean Was the command executed successfully?
 	 */
-	public static function rollback()
+	public static function rollback(): bool
 	{
 		return DI::dba()->rollback();
 	}
@@ -392,7 +391,7 @@ class DBA
 	 * @return boolean was the delete successful?
 	 * @throws \Exception
 	 */
-	public static function delete($table, array $conditions, array $options = [])
+	public static function delete($table, array $conditions, array $options = []): bool
 	{
 		return DI::dba()->delete($table, $conditions, $options);
 	}
@@ -427,7 +426,7 @@ class DBA
 	 * @return boolean was the update successfull?
 	 * @throws \Exception
 	 */
-	public static function update($table, array $fields, array $condition, $old_fields = [], array $params = [])
+	public static function update($table, array $fields, array $condition, $old_fields = [], array $params = []): bool
 	{
 		return DI::dba()->update($table, $fields, $condition, $old_fields, $params);
 	}
@@ -528,7 +527,7 @@ class DBA
 	 * @param string|array $tables
 	 * @return string
 	 */
-	public static function buildTableString($tables)
+	public static function buildTableString($tables): string
 	{
 		if (is_string($tables)) {
 			$tables = [$tables];
@@ -553,7 +552,7 @@ class DBA
 	 * @param $identifier
 	 * @return string
 	 */
-	public static function quoteIdentifier($identifier)
+	public static function quoteIdentifier(string $identifier): string
 	{
 		return '`' . str_replace('`', '``', $identifier) . '`';
 	}
@@ -576,7 +575,7 @@ class DBA
 	 * @param array $condition
 	 * @return string
 	 */
-	public static function buildCondition(array &$condition = [])
+	public static function buildCondition(array &$condition = []): string
 	{
 		$condition = self::collapseCondition($condition);
 		
@@ -600,7 +599,7 @@ class DBA
 	 * @param array $condition
 	 * @return array
 	 */
-	public static function collapseCondition(array $condition)
+	public static function collapseCondition(array $condition): array
 	{
 		// Ensures an always true condition is returned
 		if (count($condition) < 1) {
@@ -675,7 +674,7 @@ class DBA
 	 * @return array A collapsed condition
 	 * @see DBA::collapseCondition() for the condition array formats
 	 */
-	public static function mergeConditions(array ...$conditions)
+	public static function mergeConditions(array ...$conditions): array
 	{
 		if (count($conditions) == 1) {
 			return current($conditions);
@@ -724,7 +723,7 @@ class DBA
 	 * @param array $params
 	 * @return string
 	 */
-	public static function buildParameter(array $params = [])
+	public static function buildParameter(array $params = []): string
 	{
 		$groupby_string = '';
 		if (!empty($params['group_by'])) {
@@ -771,7 +770,7 @@ class DBA
 	 *
 	 * @return array Data array
 	 */
-	public static function toArray($stmt, $do_close = true, int $count = 0): array
+	public static function toArray($stmt, bool $do_close = true, int $count = 0): array
 	{
 		return DI::dba()->toArray($stmt, $do_close, $count);
 	}
@@ -847,10 +846,9 @@ class DBA
 	 * Checks if $array is a filled array with at least one entry.
 	 *
 	 * @param mixed $array A filled array with at least one entry
-	 *
 	 * @return boolean Whether $array is a filled array or an object with rows
 	 */
-	public static function isResult($array)
+	public static function isResult($array): bool
 	{
 		return DI::dba()->isResult($array);
 	}
@@ -862,7 +860,7 @@ class DBA
 	 * @param boolean $add_quotation add quotation marks for string values
 	 * @return void
 	 */
-	public static function escapeArray(&$arr, $add_quotation = false)
+	public static function escapeArray(&$arr, bool $add_quotation = false)
 	{
 		DI::dba()->escapeArray($arr, $add_quotation);
 	}
diff --git a/src/Database/Database.php b/src/Database/Database.php
index d1aff8221..8c2cd0241 100644
--- a/src/Database/Database.php
+++ b/src/Database/Database.php
@@ -26,6 +26,7 @@ use Friendica\Core\System;
 use Friendica\Network\HTTPException\ServiceUnavailableException;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Profiler;
+use InvalidArgumentException;
 use mysqli;
 use mysqli_result;
 use mysqli_stmt;
@@ -88,7 +89,12 @@ class Database
 		}
 	}
 
-	public function connect()
+	/**
+	 * Tries to connect to database
+	 *
+	 * @return bool Success
+	 */
+	public function connect(): bool
 	{
 		if (!is_null($this->connection) && $this->connected()) {
 			return $this->connected;
@@ -255,7 +261,7 @@ class Database
 	 *
 	 * @return string with either "pdo" or "mysqli"
 	 */
-	public function getDriver()
+	public function getDriver(): string
 	{
 		return $this->driver;
 	}
@@ -266,9 +272,9 @@ class Database
 	 * This function discriminate between the deprecated mysql API and the current
 	 * object-oriented mysqli API. Example of returned string: 5.5.46-0+deb8u1
 	 *
-	 * @return string
+	 * @return string Database server information
 	 */
-	public function serverInfo()
+	public function serverInfo(): string
 	{
 		if ($this->server_info == '') {
 			switch ($this->driver) {
@@ -286,10 +292,10 @@ class Database
 	/**
 	 * Returns the selected database name
 	 *
-	 * @return string
+	 * @return string Database name
 	 * @throws \Exception
 	 */
-	public function databaseName()
+	public function databaseName(): string
 	{
 		$ret  = $this->p("SELECT DATABASE() AS `db`");
 		$data = $this->toArray($ret);
@@ -300,10 +306,10 @@ class Database
 	 * Analyze a database query and log this if some conditions are met.
 	 *
 	 * @param string $query The database query that will be analyzed
-	 *
+	 * @return void
 	 * @throws \Exception
 	 */
-	private function logIndex($query)
+	private function logIndex(string $query)
 	{
 
 		if (!$this->configCache->get('system', 'db_log_index')) {
@@ -359,11 +365,10 @@ class Database
 	 * Removes every not allowlisted character from the identifier string
 	 *
 	 * @param string $identifier
-	 *
 	 * @return string sanitized identifier
 	 * @throws \Exception
 	 */
-	private function sanitizeIdentifier($identifier)
+	private function sanitizeIdentifier(string $identifier): string
 	{
 		return preg_replace('/[^A-Za-z0-9_\-]+/', '', $identifier);
 	}
@@ -383,11 +388,21 @@ class Database
 		}
 	}
 
-	public function isConnected()
+	/**
+	 * Returns connected flag
+	 *
+	 * @return bool Whether connection to database was success
+	 */
+	public function isConnected(): bool
 	{
 		return $this->connected;
 	}
 
+	/**
+	 * Checks connection status
+	 *
+	 * @return bool Whether connection to database was success
+	 */
 	public function connected()
 	{
 		$connected = false;
@@ -424,7 +439,7 @@ class Database
 	 *
 	 * @return string The input SQL string modified if necessary.
 	 */
-	public function anyValueFallback($sql)
+	public function anyValueFallback(string $sql): string
 	{
 		$server_info = $this->serverInfo();
 		if (version_compare($server_info, '5.7.5', '<') ||
@@ -442,7 +457,7 @@ class Database
 	 *
 	 * @return string The replaced SQL query
 	 */
-	private function replaceParameters($sql, $args)
+	private function replaceParameters(string $sql, array $args): string
 	{
 		$offset = 0;
 		foreach ($args as $param => $value) {
@@ -476,7 +491,7 @@ class Database
 	 * @return bool|object statement object or result object
 	 * @throws \Exception
 	 */
-	public function p($sql)
+	public function p(string $sql)
 	{
 
 		$this->profiler->startRecording('database');
@@ -741,8 +756,9 @@ class Database
 	 * @return boolean Was the query successfull? False is returned only if an error occurred
 	 * @throws \Exception
 	 */
-	public function e($sql)
+	public function e(string $sql): bool
 	{
+		$retval = false;
 
 		$this->profiler->startRecording('database_write');
 
@@ -810,7 +826,7 @@ class Database
 	 * @return boolean Are there rows for that condition?
 	 * @throws \Exception
 	 */
-	public function exists($table, $condition)
+	public function exists($table, array $condition): bool
 	{
 		if (empty($table)) {
 			return false;
@@ -850,10 +866,10 @@ class Database
 	 *
 	 * @param string $sql SQL statement
 	 *
-	 * @return array first row of query
+	 * @return array|bool first row of query or false on failure
 	 * @throws \Exception
 	 */
-	public function fetchFirst($sql)
+	public function fetchFirst(string $sql)
 	{
 		$params = DBA::getParam(func_get_args());
 
@@ -875,7 +891,7 @@ class Database
 	 *
 	 * @return int Number of rows
 	 */
-	public function affectedRows()
+	public function affectedRows(): int
 	{
 		return $this->affected_rows;
 	}
@@ -887,7 +903,7 @@ class Database
 	 *
 	 * @return int Number of columns
 	 */
-	public function columnCount($stmt)
+	public function columnCount($stmt): int
 	{
 		if (!is_object($stmt)) {
 			return 0;
@@ -908,7 +924,7 @@ class Database
 	 *
 	 * @return int Number of rows
 	 */
-	public function numRows($stmt)
+	public function numRows($stmt): int
 	{
 		if (!is_object($stmt)) {
 			return 0;
@@ -927,7 +943,7 @@ class Database
 	 *
 	 * @param bool|PDOStatement|mysqli_stmt $stmt statement object
 	 *
-	 * @return array|false current row
+	 * @return array|bool Current row or false on failure
 	 */
 	public function fetch($stmt)
 	{
@@ -994,7 +1010,7 @@ class Database
 	 * @return boolean was the insert successful?
 	 * @throws \Exception
 	 */
-	public function insert($table, array $param, int $duplicate_mode = self::INSERT_DEFAULT)
+	public function insert($table, array $param, int $duplicate_mode = self::INSERT_DEFAULT): bool
 	{
 		if (empty($table) || empty($param)) {
 			$this->logger->info('Table and fields have to be set');
@@ -1044,7 +1060,7 @@ class Database
 	 * @return boolean was the insert successful?
 	 * @throws \Exception
 	 */
-	public function replace($table, array $param)
+	public function replace($table, array $param): bool
 	{
 		if (empty($table) || empty($param)) {
 			$this->logger->info('Table and fields have to be set');
@@ -1069,7 +1085,7 @@ class Database
 	 *
 	 * @return integer Last inserted id
 	 */
-	public function lastInsertId()
+	public function lastInsertId(): int
 	{
 		switch ($this->driver) {
 			case self::PDO:
@@ -1092,7 +1108,7 @@ class Database
 	 * @return boolean was the lock successful?
 	 * @throws \Exception
 	 */
-	public function lock($table)
+	public function lock($table): bool
 	{
 		// See here: https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html
 		if ($this->driver == self::PDO) {
@@ -1126,7 +1142,7 @@ class Database
 	 * @return boolean was the unlock successful?
 	 * @throws \Exception
 	 */
-	public function unlock()
+	public function unlock(): bool
 	{
 		// See here: https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html
 		$this->performCommit();
@@ -1177,7 +1193,12 @@ class Database
 		return true;
 	}
 
-	protected function performCommit()
+	/**
+	 * Performs the commit
+	 *
+	 * @return boolean Was the command executed successfully?
+	 */
+	protected function performCommit(): bool
 	{
 		switch ($this->driver) {
 			case self::PDO:
@@ -1199,7 +1220,7 @@ class Database
 	 *
 	 * @return boolean Was the command executed successfully?
 	 */
-	public function commit()
+	public function commit(): bool
 	{
 		if (!$this->performCommit()) {
 			return false;
@@ -1213,7 +1234,7 @@ class Database
 	 *
 	 * @return boolean Was the command executed successfully?
 	 */
-	public function rollback()
+	public function rollback(): bool
 	{
 		$ret = false;
 
@@ -1230,6 +1251,7 @@ class Database
 				$ret = $this->connection->rollback();
 				break;
 		}
+
 		$this->in_transaction = false;
 		return $ret;
 	}
@@ -1243,7 +1265,7 @@ class Database
 	 * @return boolean was the delete successful?
 	 * @throws \Exception
 	 */
-	public function delete($table, array $conditions)
+	public function delete($table, array $conditions): bool
 	{
 		if (empty($table) || empty($conditions)) {
 			$this->logger->info('Table and conditions have to be set');
@@ -1288,8 +1310,9 @@ class Database
 	 *
 	 * @return boolean was the update successfull?
 	 * @throws \Exception
+	 * @todo Implement "bool $update_on_duplicate" to avoid mixed type for $old_fields
 	 */
-	public function update($table, $fields, $condition, $old_fields = [], $params = [])
+	public function update($table, array $fields, array $condition, $old_fields = [], array $params = [])
 	{
 		if (empty($table) || empty($fields) || empty($condition)) {
 			$this->logger->info('Table, fields and condition have to be set');
@@ -1354,7 +1377,7 @@ class Database
 	 * @throws \Exception
 	 * @see   $this->select
 	 */
-	public function selectFirst($table, array $fields = [], array $condition = [], $params = [])
+	public function selectFirst($table, array $fields = [], array $condition = [], array $params = [])
 	{
 		$params['limit'] = 1;
 		$result          = $this->select($table, $fields, $condition, $params);
@@ -1390,9 +1413,9 @@ class Database
 	 *
 	 * @param array $fields 
 	 * @param array $options 
-	 * @return array 
+	 * @return array Escaped fields
 	 */
-	private function escapeFields(array $fields, array $options)
+	private function escapeFields(array $fields, array $options): array
 	{
 		// In the case of a "GROUP BY" we have to add all the ORDER fields to the fieldlist.
 		// This needs to done to apply the "ANY_VALUE(...)" treatment from below to them.
@@ -1490,7 +1513,7 @@ class Database
 	 * @param array        $condition Array of fields for condition
 	 * @param array        $params    Array of several parameters
 	 *
-	 * @return int
+	 * @return int Count of rows
 	 *
 	 * Example:
 	 * $table = "post";
@@ -1502,10 +1525,10 @@ class Database
 	 * $count = DBA::count($table, $condition);
 	 * @throws \Exception
 	 */
-	public function count($table, array $condition = [], array $params = [])
+	public function count($table, array $condition = [], array $params = []): int
 	{
 		if (empty($table)) {
-			return false;
+			throw new InvalidArgumentException('Parameter "table" cannot be empty.');
 		}
 
 		$table_string = DBA::buildTableString($table);
@@ -1569,7 +1592,8 @@ class Database
 	 * @param array  $fields
 	 * @return array casted fields
 	 */
-	public function castFields(string $table, array $fields) {
+	public function castFields(string $table, array $fields): array
+	{
 		// When there is no data, we don't need to do something
 		if (empty($fields)) {
 			return $fields;
@@ -1642,7 +1666,7 @@ class Database
 	 *
 	 * @return string Error message ('' if no error)
 	 */
-	public function errorMessage()
+	public function errorMessage(): string
 	{
 		return $this->error;
 	}
@@ -1729,7 +1753,7 @@ class Database
 	 * @param string $name
 	 * @return string content
 	 */
-	public function getVariable(string $name)
+	public function getVariable(string $name): string
 	{
 		$result = $this->fetchFirst("SHOW GLOBAL VARIABLES WHERE `Variable_name` = ?", $name);
 		return $result['Value'] ?? null;
@@ -1742,7 +1766,7 @@ class Database
 	 *
 	 * @return boolean Whether $array is a filled array or an object with rows
 	 */
-	public function isResult($array)
+	public function isResult($array): bool
 	{
 		// It could be a return value from an update statement
 		if (is_bool($array)) {
@@ -1762,10 +1786,9 @@ class Database
 	 * @param mixed   $value         Array value
 	 * @param string  $key           Array key
 	 * @param boolean $add_quotation add quotation marks for string values
-	 *
 	 * @return void
 	 */
-	private function escapeArrayCallback(&$value, $key, $add_quotation)
+	private function escapeArrayCallback(&$value, string $key, bool $add_quotation)
 	{
 		if (!$add_quotation) {
 			if (is_bool($value)) {
@@ -1790,10 +1813,9 @@ class Database
 	 *
 	 * @param mixed   $arr           Array with values to be escaped
 	 * @param boolean $add_quotation add quotation marks for string values
-	 *
 	 * @return void
 	 */
-	public function escapeArray(&$arr, $add_quotation = false)
+	public function escapeArray(&$arr, bool $add_quotation = false)
 	{
 		array_walk($arr, [$this, 'escapeArrayCallback'], $add_quotation);
 	}
@@ -1801,10 +1823,11 @@ class Database
 	/**
 	 * Replaces a string in the provided fields of the provided table
 	 *
-	 * @param string $table_name
+	 * @param string $table_name Table name
 	 * @param array  $fields List of field names in the provided table
 	 * @param string $search
 	 * @param string $replace
+	 * @return void
 	 * @throws \Exception
 	 */
 	public function replaceInTableFields(string $table_name, array $fields, string $search, string $replace)
diff --git a/src/Database/View.php b/src/Database/View.php
index a31151c21..c8941167e 100644
--- a/src/Database/View.php
+++ b/src/Database/View.php
@@ -39,12 +39,12 @@ class View
 	 * On first pass, defines DB_UPDATE_VERSION constant.
 	 *
 	 * @see static/dbview.config.php
-	 * @param boolean $with_addons_structure Whether to tack on addons additional tables
 	 * @param string  $basePath              The base path of this application
+	 * @param boolean $with_addons_structure Whether to tack on addons additional tables
 	 * @return array
 	 * @throws Exception
 	 */
-	public static function definition($basePath = '', $with_addons_structure = true)
+	public static function definition(string $basePath = '', bool $with_addons_structure = true): array
 	{
 		if (!self::$definition) {
 			if (empty($basePath)) {
@@ -75,6 +75,13 @@ class View
 		return $definition;
 	}
 
+	/**
+	 * Creates a view
+	 *
+	 * @param bool $verbose Whether to show SQL statements
+	 * @param bool $action Whether to execute SQL statements
+	 * @return void
+	 */
 	public static function create(bool $verbose, bool $action)
 	{
 		// Delete previously used views that aren't used anymore
@@ -94,11 +101,17 @@ class View
 		$definition = self::definition();
 
 		foreach ($definition as $name => $structure) {
-			self::createview($name, $structure, $verbose, $action);
+			self::createView($name, $structure, $verbose, $action);
 		}
 	}
 
-	public static function printStructure($basePath)
+	/**
+	 * Prints view structure
+	 *
+	 * @param string $basePath Base path
+	 * @return void
+	 */
+	public static function printStructure(string $basePath)
 	{
 		$database = self::definition($basePath, false);
 
@@ -112,12 +125,21 @@ class View
 		}
 	}
 
-	private static function createview($name, $structure, $verbose, $action)
+	/**
+	 * Creates view
+	 *
+	 * @param string $name Name of view
+	 * @param array $structure Structure of view
+	 * @param bool $verbose Whether to show SQL statements
+	 * @param bool $action Whether to execute SQL statements
+	 * @return bool Whether execution went fine
+	 */
+	private static function createView(string $name, array $structure, bool $verbose, bool $action): bool
 	{
 		$r = true;
 
 		$sql_rows = [];
-		foreach ($structure["fields"] as $fieldname => $origin) {
+		foreach ($structure['fields'] as $fieldname => $origin) {
 			if (is_string($origin)) {
 				$sql_rows[] = $origin . " AS `" . DBA::escape($fieldname) . "`";
 			} elseif (is_array($origin) && (sizeof($origin) == 2)) {
@@ -159,7 +181,7 @@ class View
 	 * @param string $view
 	 * @return boolean "true" if it's a view
 	 */
-	private static function isView(string $view)
+	private static function isView(string $view): bool
 	{
 		$status = DBA::selectFirst(['INFORMATION_SCHEMA' => 'TABLES'], ['TABLE_TYPE'],
 			['TABLE_SCHEMA' => DBA::databaseName(), 'TABLE_NAME' => $view]);
@@ -177,7 +199,7 @@ class View
 	 * @param string $table
 	 * @return boolean "true" if it's a table
 	 */
-	private static function isTable(string $table)
+	private static function isTable(string $table): bool
 	{
 		$status = DBA::selectFirst(['INFORMATION_SCHEMA' => 'TABLES'], ['TABLE_TYPE'],
 			['TABLE_SCHEMA' => DBA::databaseName(), 'TABLE_NAME' => $table]);
diff --git a/src/Factory/Api/Mastodon/Status.php b/src/Factory/Api/Mastodon/Status.php
index 5d5894415..0fc9281db 100644
--- a/src/Factory/Api/Mastodon/Status.php
+++ b/src/Factory/Api/Mastodon/Status.php
@@ -190,7 +190,7 @@ class Status extends BaseFactory
 	 */
 	public function createFromMailId(int $id): \Friendica\Object\Api\Mastodon\Status
 	{
-		$item = ActivityPub\Transmitter::ItemArrayFromMail($id, true);
+		$item = ActivityPub\Transmitter::getItemArrayFromMail($id, true);
 		if (empty($item)) {
 			$this->mstdnErrorFactory->RecordNotFound();
 		}
diff --git a/src/Model/APContact.php b/src/Model/APContact.php
index 5c1d962a8..9269ee790 100644
--- a/src/Model/APContact.php
+++ b/src/Model/APContact.php
@@ -116,6 +116,7 @@ class APContact
 	 * @return array profile array
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
+	 * @todo Rewrite parameter $update to avoid true|false|null (boolean is binary, null adds a third case)
 	 */
 	public static function getByURL(string $url, $update = null): array
 	{
diff --git a/src/Model/GServer.php b/src/Model/GServer.php
index e5c1bb3b6..f6c5e14af 100644
--- a/src/Model/GServer.php
+++ b/src/Model/GServer.php
@@ -918,8 +918,11 @@ class GServer
 			return [];
 		}
 
-		$server = ['detection-method' => self::DETECT_NODEINFO_2,
-			'register_policy' => Register::CLOSED];
+		$server = [
+			'detection-method' => self::DETECT_NODEINFO_2,
+			'register_policy' => Register::CLOSED,
+			'platform' => 'unknown',
+		];
 
 		if (!empty($nodeinfo['openRegistrations'])) {
 			$server['register_policy'] = Register::OPEN;
diff --git a/src/Model/Item.php b/src/Model/Item.php
index 1e3326e28..5144e73e0 100644
--- a/src/Model/Item.php
+++ b/src/Model/Item.php
@@ -1841,13 +1841,13 @@ class Item
 		$parsed = parse_url($uri);
 
 		// Remove the scheme to make sure that "https" and "http" doesn't make a difference
-		unset($parsed["scheme"]);
+		unset($parsed['scheme']);
 
 		// Glue it together to be able to make a hash from it
-		$host_id = implode("/", $parsed);
+		$host_id = implode('/', $parsed);
 
 		// Use a mixture of several hashes to provide some GUID like experience
-		return hash("crc32", $host) . '-'. hash('joaat', $host_id) . '-'. hash('fnv164', $host_id);
+		return hash('crc32', $host) . '-'. hash('joaat', $host_id) . '-'. hash('fnv164', $host_id);
 	}
 
 	/**
@@ -1859,9 +1859,9 @@ class Item
 	 * @return string
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function newURI($uid, $guid = "")
+	public static function newURI(int $uid, string $guid = ''): string
 	{
-		if ($guid == "") {
+		if ($guid == '') {
 			$guid = System::createUUID();
 		}
 
diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index eab23222c..0b58427c3 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -1245,6 +1245,7 @@ class Processor
 	 * perform a "follow" request
 	 *
 	 * @param array $activity
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
@@ -1296,8 +1297,8 @@ class Processor
 	/**
 	 * Transmit pending events to the new follower
 	 *
-	 * @param integer $cid
-	 * @param integer $uid
+	 * @param integer $cid Contact id
+	 * @param integer $uid User id
 	 * @return void
 	 */
 	private static function transmitPendingEvents(int $cid, int $uid)
@@ -1340,6 +1341,7 @@ class Processor
 	 * Delete the given profile
 	 *
 	 * @param array $activity
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
 	public static function deletePerson(array $activity)
@@ -1367,6 +1369,7 @@ class Processor
 	 * Blocks the user by the contact
 	 *
 	 * @param array $activity
+	 * @return void
 	 * @throws \Exception
 	 */
 	public static function blockAccount(array $activity)
@@ -1390,6 +1393,7 @@ class Processor
 	 * Unblocks the user by the contact
 	 *
 	 * @param array $activity
+	 * @return void
 	 * @throws \Exception
 	 */
 	public static function unblockAccount(array $activity)
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index be1c3b7e7..38b6c4fc5 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -80,13 +80,13 @@ class Receiver
 	/**
 	 * Checks incoming message from the inbox
 	 *
-	 * @param         $body
-	 * @param         $header
+	 * @param string  $body Body string
+	 * @param array   $header Header lines
 	 * @param integer $uid User ID
+	 * @return void
 	 * @throws \Exception
-	 * @todo Find type for $body/$header
 	 */
-	public static function processInbox($body, $header, int $uid)
+	public static function processInbox(string $body, array $header, int $uid)
 	{
 		$activity = json_decode($body, true);
 		if (empty($activity)) {
@@ -96,9 +96,9 @@ class Receiver
 
 		$ldactivity = JsonLD::compact($activity);
 
-		$actor = JsonLD::fetchElement($ldactivity, 'as:actor', '@id');
-
+		$actor = JsonLD::fetchElement($ldactivity, 'as:actor', '@id') ?? '';
 		$apcontact = APContact::getByURL($actor);
+
 		if (empty($apcontact)) {
 			Logger::notice('Unable to retrieve AP contact for actor - message is discarded', ['actor' => $actor]);
 			return;
diff --git a/src/Protocol/ActivityPub/Transmitter.php b/src/Protocol/ActivityPub/Transmitter.php
index 8483d5d1d..6384e2ed4 100644
--- a/src/Protocol/ActivityPub/Transmitter.php
+++ b/src/Protocol/ActivityPub/Transmitter.php
@@ -103,12 +103,12 @@ class Transmitter
 	}
 
 	/**
-	 * Subscribe to a relay
+	 * Subscribe to a relay and updates contact on success
 	 *
 	 * @param string $url Subscribe actor url
 	 * @return bool success
 	 */
-	public static function sendRelayFollow(string $url)
+	public static function sendRelayFollow(string $url): bool
 	{
 		$contact = Contact::getByURL($url);
 		if (empty($contact)) {
@@ -125,13 +125,13 @@ class Transmitter
 	}
 
 	/**
-	 * Unsubscribe from a relay
+	 * Unsubscribe from a relay and updates contact on success or forced
 	 *
 	 * @param string $url   Subscribe actor url
 	 * @param bool   $force Set the relay status as non follower even if unsubscribe hadn't worked
 	 * @return bool success
 	 */
-	public static function sendRelayUndoFollow(string $url, bool $force = false)
+	public static function sendRelayUndoFollow(string $url, bool $force = false): bool
 	{
 		$contact = Contact::getByURL($url);
 		if (empty($contact)) {
@@ -139,6 +139,7 @@ class Transmitter
 		}
 
 		$success = self::sendContactUndo($url, $contact['id'], 0);
+
 		if ($success || $force) {
 			Contact::update(['rel' => Contact::NOTHING], ['id' => $contact['id']]);
 		}
@@ -155,11 +156,10 @@ class Transmitter
 	 * @param integer $page      Page number
 	 * @param string  $requester URL of the requester
 	 * @param boolean $nocache   Wether to bypass caching
-	 *
 	 * @return array of owners
 	 * @throws \Exception
 	 */
-	public static function getContacts(array $owner, array $rel, string $module, int $page = null, string $requester = null, $nocache = false)
+	public static function getContacts(array $owner, array $rel, string $module, int $page = null, string $requester = null, bool $nocache = false): array
 	{
 		if (empty($page)) {
 			$cachekey = self::CACHEKEY_CONTACTS . $module . ':'. $owner['uid'];
@@ -246,12 +246,11 @@ class Transmitter
 	 * @param integer $page      Page number
 	 * @param string  $requester URL of requesting account
 	 * @param boolean $nocache   Wether to bypass caching
-	 *
 	 * @return array of posts
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function getOutbox(array $owner, int $page = null, string $requester = '', $nocache = false)
+	public static function getOutbox(array $owner, int $page = null, string $requester = '', bool $nocache = false): array
 	{
 		if (empty($page)) {
 			$cachekey = self::CACHEKEY_OUTBOX . $owner['uid'];
@@ -274,15 +273,16 @@ class Transmitter
 			}
 		}
 
-		$condition = array_merge($condition,
-			['uid'           => $owner['uid'],
+		$condition = array_merge($condition, [
+			'uid'           => $owner['uid'],
 			'author-id'      => Contact::getIdForURL($owner['url'], 0, false),
 			'gravity'        => [GRAVITY_PARENT, GRAVITY_COMMENT],
 			'network'        => Protocol::FEDERATED,
 			'parent-network' => Protocol::FEDERATED,
 			'origin'         => true,
 			'deleted'        => false,
-			'visible'        => true]);
+			'visible'        => true
+		]);
 
 		$count = Post::count($condition);
 
@@ -340,7 +340,7 @@ class Transmitter
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function getFeatured(array $owner, int $page = null, $nocache = false)
+	public static function getFeatured(array $owner, int $page = null, bool $nocache = false): array
 	{
 		if (empty($page)) {
 			$cachekey = self::CACHEKEY_FEATURED . $owner['uid'];
@@ -355,8 +355,8 @@ class Transmitter
 		$condition = ["`uri-id` IN (SELECT `uri-id` FROM `collection-view` WHERE `cid` = ? AND `type` = ?)",
 			$owner_cid, Post\Collection::FEATURED];
 
-		$condition = DBA::mergeConditions($condition,
-			['uid'           => $owner['uid'],
+		$condition = DBA::mergeConditions($condition, [
+			'uid'           => $owner['uid'],
 			'author-id'      => $owner_cid,
 			'private'        => [Item::PUBLIC, Item::UNLISTED],
 			'gravity'        => [GRAVITY_PARENT, GRAVITY_COMMENT],
@@ -364,7 +364,8 @@ class Transmitter
 			'parent-network' => Protocol::FEDERATED,
 			'origin'         => true,
 			'deleted'        => false,
-			'visible'        => true]);
+			'visible'        => true
+		]);
 
 		$count = Post::count($condition);
 
@@ -418,11 +419,13 @@ class Transmitter
 	 *
 	 * @return array with service data
 	 */
-	private static function getService()
+	private static function getService(): array
 	{
-		return ['type' => 'Service',
+		return [
+			'type' => 'Service',
 			'name' =>  FRIENDICA_PLATFORM . " '" . FRIENDICA_CODENAME . "' " . FRIENDICA_VERSION . '-' . DB_UPDATE_VERSION,
-			'url' => DI::baseUrl()->get()];
+			'url' => DI::baseUrl()->get()
+		];
 	}
 
 	/**
@@ -537,7 +540,7 @@ class Transmitter
 	 * @return array
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function getDeletedUser($username)
+	public static function getDeletedUser(string $username): array
 	{
 		return [
 			'@context' => ActivityPub::CONTEXT,
@@ -559,7 +562,7 @@ class Transmitter
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	private static function fetchPermissionBlockFromThreadParent(array $item, bool $is_forum_thread)
+	private static function fetchPermissionBlockFromThreadParent(array $item, bool $is_forum_thread): array
 	{
 		if (empty($item['thr-parent-id'])) {
 			return [];
@@ -606,7 +609,7 @@ class Transmitter
 	 * @param integer $item_id
 	 * @return boolean "true" if the post is from ActivityPub
 	 */
-	private static function isAPPost(int $item_id)
+	private static function isAPPost(int $item_id): bool
 	{
 		if (empty($item_id)) {
 			return false;
@@ -626,7 +629,7 @@ class Transmitter
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	private static function createPermissionBlockForItem($item, $blindcopy, $last_id = 0)
+	private static function createPermissionBlockForItem(array $item, bool $blindcopy, int $last_id = 0): array
 	{
 		if ($last_id == 0) {
 			$last_id = $item['id'];
@@ -858,10 +861,9 @@ class Transmitter
 	 * Check if an inbox is archived
 	 *
 	 * @param string $url Inbox url
-	 *
 	 * @return boolean "true" if inbox is archived
 	 */
-	public static function archivedInbox($url)
+	public static function archivedInbox(string $url): bool
 	{
 		return DBA::exists('inbox-status', ['url' => $url, 'archive' => true]);
 	}
@@ -869,12 +871,12 @@ class Transmitter
 	/**
 	 * Check if a given contact should be delivered via AP
 	 *
-	 * @param array $contact
-	 * @param array $networks
-	 * @return bool
+	 * @param array $contact Contact array
+	 * @param array $networks Array with networks
+	 * @return bool Whether the used protocol matches ACTIVITYPUB
 	 * @throws Exception
 	 */
-	private static function isAPContact(array $contact, array $networks)
+	private static function isAPContact(array $contact, array $networks): bool
 	{
 		if (in_array($contact['network'], $networks) || ($contact['protocol'] == Protocol::ACTIVITYPUB)) {
 			return true;
@@ -889,12 +891,11 @@ class Transmitter
 	 * @param integer $uid      User ID
 	 * @param boolean $personal fetch personal inboxes
 	 * @param boolean $all_ap   Retrieve all AP enabled inboxes
-	 *
 	 * @return array of follower inboxes
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function fetchTargetInboxesforUser($uid, $personal = false, bool $all_ap = false)
+	public static function fetchTargetInboxesforUser(int $uid, bool $personal = false, bool $all_ap = false): array
 	{
 		$inboxes = [];
 
@@ -963,7 +964,7 @@ class Transmitter
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function fetchTargetInboxes($item, $uid, $personal = false, $last_id = 0)
+	public static function fetchTargetInboxes(array $item, int $uid, bool $personal = false, int $last_id = 0): array
 	{
 		$permissions = self::createPermissionBlockForItem($item, true, $last_id);
 		if (empty($permissions)) {
@@ -1022,12 +1023,11 @@ class Transmitter
 	/**
 	 * Creates an array in the structure of the item table for a given mail id
 	 *
-	 * @param integer $mail_id
-	 *
+	 * @param integer $mail_id Mail id
 	 * @return array
 	 * @throws \Exception
 	 */
-	public static function ItemArrayFromMail($mail_id, $use_title = false)
+	public static function getItemArrayFromMail(int $mail_id, bool $use_title = false): array
 	{
 		$mail = DBA::selectFirst('mail', [], ['id' => $mail_id]);
 		if (!DBA::isResult($mail)) {
@@ -1079,9 +1079,9 @@ class Transmitter
 	 * @return array of activity
 	 * @throws \Exception
 	 */
-	public static function createActivityFromMail($mail_id, $object_mode = false)
+	public static function createActivityFromMail(int $mail_id, bool $object_mode = false): array
 	{
-		$mail = self::ItemArrayFromMail($mail_id);
+		$mail = self::getItemArrayFromMail($mail_id);
 		if (empty($mail)) {
 			return [];
 		}
@@ -1133,18 +1133,17 @@ class Transmitter
 	/**
 	 * Returns the activity type of a given item
 	 *
-	 * @param array $item
-	 *
+	 * @param array $item Item array
 	 * @return string with activity type
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	private static function getTypeOfItem($item)
+	private static function getTypeOfItem(array $item): string
 	{
 		$reshared = false;
 
 		// Only check for a reshare, if it is a real reshare and no quoted reshare
-		if (strpos($item['body'], "[share") === 0) {
+		if (strpos($item['body'], '[share') === 0) {
 			$announce = self::getAnnounceArray($item);
 			$reshared = !empty($announce);
 		}
@@ -1183,13 +1182,12 @@ class Transmitter
 	/**
 	 * Creates the activity or fetches it from the cache
 	 *
-	 * @param integer $item_id
+	 * @param integer $item_id Item id
 	 * @param boolean $force Force new cache entry
-	 *
 	 * @return array with the activity
 	 * @throws \Exception
 	 */
-	public static function createCachedActivityFromItem($item_id, $force = false)
+	public static function createCachedActivityFromItem(int $item_id, bool $force = false): array
 	{
 		$cachekey = 'APDelivery:createActivity:' . $item_id;
 
@@ -1211,7 +1209,6 @@ class Transmitter
 	 *
 	 * @param integer $item_id
 	 * @param boolean $object_mode Is the activity item is used inside another object?
-	 *
 	 * @return false|array
 	 * @throws \Exception
 	 */
@@ -1335,11 +1332,10 @@ class Transmitter
 	/**
 	 * Creates a location entry for a given item array
 	 *
-	 * @param array $item
-	 *
+	 * @param array $item Item array
 	 * @return array with location array
 	 */
-	private static function createLocation($item)
+	private static function createLocation(array $item): array
 	{
 		$location = ['type' => 'Place'];
 
@@ -1369,12 +1365,11 @@ class Transmitter
 	/**
 	 * Returns a tag array for a given item array
 	 *
-	 * @param array $item
-	 *
+	 * @param array $item Item array
 	 * @return array of tags
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	private static function createTagList($item)
+	private static function createTagList(array $item): array
 	{
 		$tags = [];
 
@@ -1416,7 +1411,7 @@ class Transmitter
 	 * @return array with attachment data
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	private static function createAttachmentList($item, $type)
+	private static function createAttachmentList(array $item, string $type): array
 	{
 		$attachments = [];
 
@@ -1468,7 +1463,7 @@ class Transmitter
 	 * @return string Replaced mention
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	private static function mentionAddrCallback($match)
+	private static function mentionAddrCallback(array $match): string
 	{
 		if (empty($match[1])) {
 			return '';
@@ -1485,11 +1480,10 @@ class Transmitter
 	/**
 	 * Remove image elements since they are added as attachment
 	 *
-	 * @param string $body
-	 *
+	 * @param string $body HTML code
 	 * @return string with removed images
 	 */
-	private static function removePictures($body)
+	private static function removePictures(string $body): string
 	{
 		// Simplify image codes
 		$body = preg_replace("/\[img\=([0-9]*)x([0-9]*)\](.*?)\[\/img\]/ism", '[img]$3[/img]', $body);
@@ -1518,12 +1512,11 @@ class Transmitter
 	/**
 	 * Fetches the "context" value for a givem item array from the "conversation" table
 	 *
-	 * @param array $item
-	 *
+	 * @param array $item Item array
 	 * @return string with context url
 	 * @throws \Exception
 	 */
-	private static function fetchContextURLForItem($item)
+	private static function fetchContextURLForItem(array $item): string
 	{
 		$conversation = DBA::selectFirst('conversation', ['conversation-href', 'conversation-uri'], ['item-uri' => $item['parent-uri']]);
 		if (DBA::isResult($conversation) && !empty($conversation['conversation-href'])) {
@@ -1539,12 +1532,11 @@ class Transmitter
 	/**
 	 * Returns if the post contains sensitive content ("nsfw")
 	 *
-	 * @param integer $uri_id
-	 *
-	 * @return boolean
+	 * @param integer $uri_id URI id
+	 * @return boolean Whether URI id was found
 	 * @throws \Exception
 	 */
-	private static function isSensitive($uri_id)
+	private static function isSensitive(int $uri_id): bool
 	{
 		return DBA::exists('tag-view', ['uri-id' => $uri_id, 'name' => 'nsfw', 'type' => Tag::HASHTAG]);
 	}
@@ -1552,12 +1544,11 @@ class Transmitter
 	/**
 	 * Creates event data
 	 *
-	 * @param array $item
-	 *
+	 * @param array $item Item array
 	 * @return array with the event data
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	private static function createEvent($item)
+	private static function createEvent(array $item): array
 	{
 		$event = [];
 		$event['name'] = $item['event-summary'];
@@ -1583,12 +1574,11 @@ class Transmitter
 	 * Creates a note/article object array
 	 *
 	 * @param array $item
-	 *
 	 * @return array with the object data
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function createNote($item)
+	public static function createNote(array $item): array
 	{
 		if (empty($item)) {
 			return [];
@@ -1739,10 +1729,9 @@ class Transmitter
 	 * Fetches the language from the post, the user or the system.
 	 *
 	 * @param array $item
-	 *
 	 * @return string language string
 	 */
-	private static function getLanguage(array $item)
+	private static function getLanguage(array $item): string
 	{
 		// Try to fetch the language from the post itself
 		if (!empty($item['language'])) {
@@ -1767,74 +1756,71 @@ class Transmitter
 	/**
 	 * Creates an an "add tag" entry
 	 *
-	 * @param array $item
-	 * @param array $data activity data
-	 *
+	 * @param array $item Item array
+	 * @param array $activity activity data
 	 * @return array with activity data for adding tags
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	private static function createAddTag($item, $data)
+	private static function createAddTag(array $item, array $activity): array
 	{
 		$object = XML::parseString($item['object']);
-		$target = XML::parseString($item["target"]);
+		$target = XML::parseString($item['target']);
 
-		$data['diaspora:guid'] = $item['guid'];
-		$data['actor'] = $item['author-link'];
-		$data['target'] = (string)$target->id;
-		$data['summary'] = BBCode::toPlaintext($item['body']);
-		$data['object'] = ['id' => (string)$object->id, 'type' => 'tag', 'name' => (string)$object->title, 'content' => (string)$object->content];
+		$activity['diaspora:guid'] = $item['guid'];
+		$activity['actor'] = $item['author-link'];
+		$activity['target'] = (string)$target->id;
+		$activity['summary'] = BBCode::toPlaintext($item['body']);
+		$activity['object'] = ['id' => (string)$object->id, 'type' => 'tag', 'name' => (string)$object->title, 'content' => (string)$object->content];
 
-		return $data;
+		return $activity;
 	}
 
 	/**
 	 * Creates an announce object entry
 	 *
-	 * @param array $item
-	 * @param array $data activity data
-	 *
+	 * @param array $item Item array
+	 * @param array $activity activity data
 	 * @return array with activity data
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	private static function createAnnounce($item, $data)
+	private static function createAnnounce(array $item, array $activity): array
 	{
 		$orig_body = $item['body'];
 		$announce = self::getAnnounceArray($item);
 		if (empty($announce)) {
-			$data['type'] = 'Create';
-			$data['object'] = self::createNote($item);
-			return $data;
+			$activity['type'] = 'Create';
+			$activity['object'] = self::createNote($item);
+			return $activity;
 		}
 
 		if (empty($announce['comment'])) {
 			// Pure announce, without a quote
-			$data['type'] = 'Announce';
-			$data['object'] = $announce['object']['uri'];
-			return $data;
+			$activity['type'] = 'Announce';
+			$activity['object'] = $announce['object']['uri'];
+			return $activity;
 		}
 
 		// Quote
-		$data['type'] = 'Create';
+		$activity['type'] = 'Create';
 		$item['body'] = $announce['comment'] . "\n" . $announce['object']['plink'];
-		$data['object'] = self::createNote($item);
+		$activity['object'] = self::createNote($item);
 
 		/// @todo Finally descide how to implement this in AP. This is a possible way:
-		$data['object']['attachment'][] = self::createNote($announce['object']);
+		$activity['object']['attachment'][] = self::createNote($announce['object']);
 
-		$data['object']['source']['content'] = $orig_body;
-		return $data;
+		$activity['object']['source']['content'] = $orig_body;
+		return $activity;
 	}
 
 	/**
 	 * Return announce related data if the item is an annunce
 	 *
 	 * @param array $item
-	 *
-	 * @return array
+	 * @return array Announcement array
 	 */
-	public static function getAnnounceArray($item)
+	public static function getAnnounceArray(array $item): array
 	{
 		$reshared = Item::getShareArray($item);
 		if (empty($reshared['guid'])) {
@@ -1861,11 +1847,10 @@ class Transmitter
 	/**
 	 * Checks if the provided item array is an announce
 	 *
-	 * @param array $item
-	 *
-	 * @return boolean
+	 * @param array $item Item array
+	 * @return boolean Whether item is an announcement
 	 */
-	public static function isAnnounce($item)
+	public static function isAnnounce(array $item): bool
 	{
 		if (!empty($item['verb']) && ($item['verb'] == Activity::ANNOUNCE)) {
 			return true;
@@ -1886,7 +1871,7 @@ class Transmitter
 	 *
 	 * @return bool|string activity id
 	 */
-	public static function activityIDFromContact($cid)
+	public static function activityIDFromContact(int $cid)
 	{
 		$contact = DBA::selectFirst('contact', ['uid', 'id', 'created'], ['id' => $cid]);
 		if (!DBA::isResult($contact)) {
@@ -1904,17 +1889,17 @@ class Transmitter
 	 * @param integer $uid           User ID
 	 * @param string  $inbox         Target inbox
 	 * @param integer $suggestion_id Suggestion ID
-	 *
 	 * @return boolean was the transmission successful?
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function sendContactSuggestion($uid, $inbox, $suggestion_id)
+	public static function sendContactSuggestion(int $uid, string $inbox, int $suggestion_id): bool
 	{
 		$owner = User::getOwnerDataById($uid);
 
 		$suggestion = DI::fsuggest()->selectOneById($suggestion_id);
 
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => DI::baseUrl() . '/activity/' . System::createGUID(),
 			'type' => 'Announce',
 			'actor' => $owner['url'],
@@ -1922,7 +1907,8 @@ class Transmitter
 			'content' => $suggestion->note,
 			'instrument' => self::getService(),
 			'to' => [ActivityPub::PUBLIC_COLLECTION],
-			'cc' => []];
+			'cc' => []
+		];
 
 		$signed = LDSignature::sign($data, $owner);
 
@@ -1935,15 +1921,15 @@ class Transmitter
 	 *
 	 * @param integer $uid   User ID
 	 * @param string  $inbox Target inbox
-	 *
 	 * @return boolean was the transmission successful?
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function sendProfileRelocation($uid, $inbox)
+	public static function sendProfileRelocation(int $uid, string $inbox): bool
 	{
 		$owner = User::getOwnerDataById($uid);
 
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => DI::baseUrl() . '/activity/' . System::createGUID(),
 			'type' => 'dfrn:relocate',
 			'actor' => $owner['url'],
@@ -1951,7 +1937,8 @@ class Transmitter
 			'published' => DateTimeFormat::utcNow(DateTimeFormat::ATOM),
 			'instrument' => self::getService(),
 			'to' => [ActivityPub::PUBLIC_COLLECTION],
-			'cc' => []];
+			'cc' => []
+		];
 
 		$signed = LDSignature::sign($data, $owner);
 
@@ -1964,11 +1951,10 @@ class Transmitter
 	 *
 	 * @param integer $uid   User ID
 	 * @param string  $inbox Target inbox
-	 *
 	 * @return boolean was the transmission successful?
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function sendProfileDeletion($uid, $inbox)
+	public static function sendProfileDeletion(int $uid, string $inbox): bool
 	{
 		$owner = User::getOwnerDataById($uid);
 
@@ -2003,7 +1989,6 @@ class Transmitter
 	 *
 	 * @param integer $uid   User ID
 	 * @param string  $inbox Target inbox
-	 *
 	 * @return boolean was the transmission successful?
 	 * @throws HTTPException\InternalServerErrorException
 	 * @throws HTTPException\NotFoundException
@@ -2036,17 +2021,18 @@ class Transmitter
 	 * @param string  $activity Type name
 	 * @param string  $target   Target profile
 	 * @param integer $uid      User ID
+	 * @param string  $id Activity-identifier
 	 * @return bool
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 * @throws \Exception
 	 */
-	public static function sendActivity($activity, $target, $uid, $id = '')
+	public static function sendActivity(string $activity, string $target, int $uid, string $id = ''): bool
 	{
 		$profile = APContact::getByURL($target);
 		if (empty($profile['inbox'])) {
 			Logger::warning('No inbox found for target', ['target' => $target, 'profile' => $profile]);
-			return;
+			return false;
 		}
 
 		$owner = User::getOwnerDataById($uid);
@@ -2055,13 +2041,15 @@ class Transmitter
 			$id = DI::baseUrl() . '/activity/' . System::createGUID();
 		}
 
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => $id,
 			'type' => $activity,
 			'actor' => $owner['url'],
 			'object' => $profile['url'],
 			'instrument' => self::getService(),
-			'to' => [$profile['url']]];
+			'to' => [$profile['url']],
+		];
 
 		Logger::info('Sending activity ' . $activity . ' to ' . $target . ' for user ' . $uid);
 
@@ -2081,12 +2069,12 @@ class Transmitter
 	 * @throws \ImagickException
 	 * @throws \Exception
 	 */
-	public static function sendFollowObject($object, $target, $uid = 0)
+	public static function sendFollowObject(string $object, string $target, int $uid = 0): bool
 	{
 		$profile = APContact::getByURL($target);
 		if (empty($profile['inbox'])) {
 			Logger::warning('No inbox found for target', ['target' => $target, 'profile' => $profile]);
-			return;
+			return false;
 		}
 
 		if (empty($uid)) {
@@ -2108,13 +2096,15 @@ class Transmitter
 
 		$owner = User::getOwnerDataById($uid);
 
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => DI::baseUrl() . '/activity/' . System::createGUID(),
 			'type' => 'Follow',
 			'actor' => $owner['url'],
 			'object' => $object,
 			'instrument' => self::getService(),
-			'to' => [$profile['url']]];
+			'to' => [$profile['url']],
+		];
 
 		Logger::info('Sending follow ' . $object . ' to ' . $target . ' for user ' . $uid);
 
@@ -2126,12 +2116,13 @@ class Transmitter
 	 * Transmit a message that the contact request had been accepted
 	 *
 	 * @param string  $target Target profile
-	 * @param         $id
+	 * @param integer $id Object id
 	 * @param integer $uid    User ID
+	 * @return void
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function sendContactAccept($target, $id, $uid)
+	public static function sendContactAccept(string $target, int $id, int $uid)
 	{
 		$profile = APContact::getByURL($target);
 		if (empty($profile['inbox'])) {
@@ -2140,7 +2131,8 @@ class Transmitter
 		}
 
 		$owner = User::getOwnerDataById($uid);
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => DI::baseUrl() . '/activity/' . System::createGUID(),
 			'type' => 'Accept',
 			'actor' => $owner['url'],
@@ -2151,7 +2143,8 @@ class Transmitter
 				'object' => $owner['url']
 			],
 			'instrument' => self::getService(),
-			'to' => [$profile['url']]];
+			'to' => [$profile['url']],
+		];
 
 		Logger::debug('Sending accept to ' . $target . ' for user ' . $uid . ' with id ' . $id);
 
@@ -2163,13 +2156,13 @@ class Transmitter
 	 * Reject a contact request or terminates the contact relation
 	 *
 	 * @param string  $target Target profile
-	 * @param         $id
+	 * @param integer $id Object id
 	 * @param integer $uid    User ID
 	 * @return bool Operation success
 	 * @throws HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 */
-	public static function sendContactReject($target, $id, $uid): bool
+	public static function sendContactReject(string $target, int $id, int $uid): bool
 	{
 		$profile = APContact::getByURL($target);
 		if (empty($profile['inbox'])) {
@@ -2178,7 +2171,8 @@ class Transmitter
 		}
 
 		$owner = User::getOwnerDataById($uid);
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => DI::baseUrl() . '/activity/' . System::createGUID(),
 			'type' => 'Reject',
 			'actor' => $owner['url'],
@@ -2189,7 +2183,8 @@ class Transmitter
 				'object' => $owner['url']
 			],
 			'instrument' => self::getService(),
-			'to' => [$profile['url']]];
+			'to' => [$profile['url']],
+		];
 
 		Logger::debug('Sending reject to ' . $target . ' for user ' . $uid . ' with id ' . $id);
 
@@ -2201,13 +2196,14 @@ class Transmitter
 	 * Transmits a message that we don't want to follow this contact anymore
 	 *
 	 * @param string  $target Target profile
+	 * @param integer $cid    Contact id
 	 * @param integer $uid    User ID
+	 * @return bool success
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 * @throws \ImagickException
 	 * @throws \Exception
-	 * @return bool success
 	 */
-	public static function sendContactUndo($target, $cid, $uid)
+	public static function sendContactUndo(string $target, int $cid, int $uid): bool
 	{
 		$profile = APContact::getByURL($target);
 		if (empty($profile['inbox'])) {
@@ -2223,15 +2219,20 @@ class Transmitter
 		$id = DI::baseUrl() . '/activity/' . System::createGUID();
 
 		$owner = User::getOwnerDataById($uid);
-		$data = ['@context' => ActivityPub::CONTEXT,
+		$data = [
+			'@context' => ActivityPub::CONTEXT,
 			'id' => $id,
 			'type' => 'Undo',
 			'actor' => $owner['url'],
-			'object' => ['id' => $object_id, 'type' => 'Follow',
+			'object' => [
+				'id' => $object_id,
+				'type' => 'Follow',
 				'actor' => $owner['url'],
-				'object' => $profile['url']],
+				'object' => $profile['url']
+			],
 			'instrument' => self::getService(),
-			'to' => [$profile['url']]];
+			'to' => [$profile['url']],
+		];
 
 		Logger::info('Sending undo to ' . $target . ' for user ' . $uid . ' with id ' . $id);
 
@@ -2239,7 +2240,15 @@ class Transmitter
 		return HTTPSignature::transmit($signed, $profile['inbox'], $uid);
 	}
 
-	private static function prependMentions($body, int $uriid, string $authorLink)
+	/**
+	 * Prepends mentions (@) to $body variable
+	 *
+	 * @param string $body HTML code
+	 * @param int    $uriid URI id
+	 * @param string $authorLink Author link
+	 * @return string HTML code with prepended mentions
+	 */
+	private static function prependMentions(string $body, int $uriid, string $authorLink): string
 	{
 		$mentions = [];
 
diff --git a/src/Protocol/Feed.php b/src/Protocol/Feed.php
index e884c8b20..15c522040 100644
--- a/src/Protocol/Feed.php
+++ b/src/Protocol/Feed.php
@@ -312,7 +312,7 @@ class Feed
 				$item['uri'] = $guid;
 
 				// Don't use the GUID value directly but instead use it as a basis for the GUID
-				$item['guid'] = Item::guidFromUri($guid, parse_url($guid, PHP_URL_HOST) ?? parse_url($item['plink'], PHP_URL_HOST));
+				$item['guid'] = Item::guidFromUri($guid, parse_url($guid, PHP_URL_HOST) ?? parse_url($item['plink'], PHP_URL_HOST) ?? '');
 			}
 
 			if (empty($item['uri'])) {
diff --git a/src/Protocol/Salmon.php b/src/Protocol/Salmon.php
index 9724f82df..98af26c15 100644
--- a/src/Protocol/Salmon.php
+++ b/src/Protocol/Salmon.php
@@ -43,7 +43,7 @@ class Salmon
 	 * @return mixed
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function getKey($uri, $keyhash)
+	public static function getKey(string $uri, string $keyhash)
 	{
 		$ret = [];
 
@@ -109,18 +109,18 @@ class Salmon
 	 * @return integer
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
-	public static function slapper($owner, $url, $slap)
+	public static function slapper(array $owner, string $url, string $slap): int
 	{
 		// does contact have a salmon endpoint?
 
 		if (!strlen($url)) {
-			return;
+			return -1;
 		}
 
 		if (!$owner['sprvkey']) {
 			Logger::notice(sprintf("user '%s' (%d) does not have a salmon private key. Send failed.",
 			$owner['name'], $owner['uid']));
-			return;
+			return -1;
 		}
 
 		Logger::info('slapper called for '.$url.'. Data: ' . $slap);
@@ -229,7 +229,7 @@ class Salmon
 	 * @return string
 	 * @throws \Exception
 	 */
-	public static function salmonKey($pubkey)
+	public static function salmonKey(string $pubkey): string
 	{
 		Crypto::pemToMe($pubkey, $modulus, $exponent);
 		return 'RSA' . '.' . Strings::base64UrlEncode($modulus, true) . '.' . Strings::base64UrlEncode($exponent, true);
diff --git a/src/Render/FriendicaSmartyEngine.php b/src/Render/FriendicaSmartyEngine.php
index 6fc8f4480..9f35fbcc4 100644
--- a/src/Render/FriendicaSmartyEngine.php
+++ b/src/Render/FriendicaSmartyEngine.php
@@ -69,7 +69,7 @@ final class FriendicaSmartyEngine extends TemplateEngine
 	/**
 	 * @inheritDoc
 	 */
-	public function replaceMacros(string $template, array $vars)
+	public function replaceMacros(string $template, array $vars): string
 	{
 		if (!Strings::startsWith($template, self::FILE_PREFIX)) {
 			$template = self::STRING_PREFIX . $template;
diff --git a/src/Render/TemplateEngine.php b/src/Render/TemplateEngine.php
index 6bfbe3197..e160192d3 100644
--- a/src/Render/TemplateEngine.php
+++ b/src/Render/TemplateEngine.php
@@ -45,6 +45,7 @@ abstract class TemplateEngine
 	 * parameter or displays them directly if it's null.
 	 *
 	 * @param array|null $errors
+	 * @return void
 	 */
 	abstract public function testInstall(array &$errors = null);
 
@@ -53,9 +54,9 @@ abstract class TemplateEngine
 	 *
 	 * @param string $template
 	 * @param array  $vars
-	 * @return string
+	 * @return string Template output with replaced macros
 	 */
-	abstract public function replaceMacros(string $template, array $vars);
+	abstract public function replaceMacros(string $template, array $vars): string;
 
 	/**
 	 * Returns the template string from a file path and an optional sub-directory from the project root
diff --git a/src/Util/Strings.php b/src/Util/Strings.php
index d2555132a..44ddc7325 100644
--- a/src/Util/Strings.php
+++ b/src/Util/Strings.php
@@ -32,11 +32,11 @@ class Strings
 	/**
 	 * Generates a pseudo-random string of hexadecimal characters
 	 *
-	 * @param int $size
-	 * @return string
+	 * @param int $size Size of string (default: 64)
+	 * @return string Pseudo-random string
 	 * @throws \Exception
 	 */
-	public static function getRandomHex($size = 64)
+	public static function getRandomHex(int $size = 64): string
 	{
 		$byte_size = ceil($size / 2);
 
@@ -51,10 +51,9 @@ class Strings
 	 * Checks, if the given string is a valid hexadecimal code
 	 *
 	 * @param string $hexCode
-	 *
 	 * @return bool
 	 */
-	public static function isHex($hexCode)
+	public static function isHex(string $hexCode): bool
 	{
 		return !empty($hexCode) ? @preg_match("/^[a-f0-9]{2,}$/i", $hexCode) && !(strlen($hexCode) & 1) : false;
 	}
@@ -75,10 +74,9 @@ class Strings
 	 * Generate a string that's random, but usually pronounceable. Used to generate initial passwords
 	 *
 	 * @param int $len	length
-	 *
 	 * @return string
 	 */
-	public static function getRandomName($len)
+	public static function getRandomName(int $len): string
 	{
 		if ($len <= 0) {
 			return '';
@@ -161,7 +159,6 @@ class Strings
 	 *
 	 * @param string $network Network name of the contact (e.g. dfrn, rss and so on)
 	 * @param string $url	  The contact url
-	 *
 	 * @return string Formatted network name
 	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
 	 */
@@ -189,7 +186,7 @@ class Strings
 	 *
 	 * @return string		Transformed string.
 	 */
-	public static function deindent(string $text, string $chr = "[\t ]", int $count = null)
+	public static function deindent(string $text, string $chr = "[\t ]", int $count = null): string
 	{
 		$lines = explode("\n", $text);
 
@@ -218,7 +215,7 @@ class Strings
 	 *
 	 * @return string	Size with measured units.
 	 */
-	public static function formatBytes($bytes, $precision = 2)
+	public static function formatBytes(int $bytes, int $precision = 2): string
 	{
 		$units = ['B', 'KB', 'MB', 'GB', 'TB'];
 		$bytes = max($bytes, 0);
@@ -233,10 +230,9 @@ class Strings
 	 * Protect percent characters in sprintf calls
 	 *
 	 * @param string $s String to transform.
-	 *
 	 * @return string	Transformed string.
 	 */
-	public static function protectSprintf($s)
+	public static function protectSprintf(string $s): string
 	{
 		return str_replace('%', '%%', $s);
 	}
@@ -246,10 +242,9 @@ class Strings
 	 *
 	 * @param string $s					URL to encode
 	 * @param boolean $strip_padding	Optional. Default false
-	 *
 	 * @return string	Encoded URL
 	 */
-	public static function base64UrlEncode($s, $strip_padding = false)
+	public static function base64UrlEncode(string $s, bool $strip_padding = false): string
 	{
 		$s = strtr(base64_encode($s), '+/', '-_');
 
@@ -262,18 +257,13 @@ class Strings
 
 	/**
 	 * Decode Base64 Encoded URL and translate -_ to +/
-	 * @param string $s URL to decode
 	 *
+	 * @param string $s URL to decode
 	 * @return string	Decoded URL
 	 * @throws \Exception
 	 */
-	public static function base64UrlDecode($s)
+	public static function base64UrlDecode(string $s): string
 	{
-		if (is_array($s)) {
-			Logger::notice('base64url_decode: illegal input: ', ['backtrace' => debug_backtrace()]);
-			return $s;
-		}
-
 		/*
 		*  // Placeholder for new rev of salmon which strips base64 padding.
 		*  // PHP base64_decode handles the un-padded input without requiring this step
@@ -297,10 +287,9 @@ class Strings
 	 * Normalize url
 	 *
 	 * @param string $url	URL to be normalized.
-	 *
 	 * @return string	Normalized URL.
 	 */
-	public static function normaliseLink($url)
+	public static function normaliseLink(string $url): string
 	{
 		$ret = str_replace(['https:', '//www.'], ['http:', '//'], $url);
 		return rtrim($ret, '/');
@@ -310,10 +299,9 @@ class Strings
 	 * Normalize OpenID identity
 	 *
 	 * @param string $s OpenID Identity
-	 *
 	 * @return string	normalized OpenId Identity
 	 */
-	public static function normaliseOpenID($s)
+	public static function normaliseOpenID(string $s): string
 	{
 		return trim(str_replace(['http://', 'https://'], ['', ''], $s), '/');
 	}
@@ -329,7 +317,7 @@ class Strings
 	 * @return boolean True if the URLs match, otherwise False
 	 *
 	 */
-	public static function compareLink($a, $b)
+	public static function compareLink(string $a, string $b): bool
 	{
 		return (strcasecmp(self::normaliseLink($a), self::normaliseLink($b)) === 0);
 	}
@@ -340,7 +328,7 @@ class Strings
 	 * @param string $uri
 	 * @return string
 	 */
-	public static function ensureQueryParameter($uri)
+	public static function ensureQueryParameter(string $uri): string
 	{
 		if (strpos($uri, '?') === false && ($pos = strpos($uri, '&')) !== false) {
 			$uri = substr($uri, 0, $pos) . '?' . substr($uri, $pos + 1);
@@ -356,7 +344,7 @@ class Strings
 	 * @param array	 $chars
 	 * @return bool
 	 */
-	public static function startsWithChars($string, array $chars)
+	public static function startsWithChars(string $string, array $chars): bool
 	{
 		$return = in_array(substr(trim($string), 0, 1), $chars);
 
@@ -371,7 +359,7 @@ class Strings
 	 * @param string $start
 	 * @return bool
 	 */
-	public static function startsWith(string $string, string $start)
+	public static function startsWith(string $string, string $start): bool
 	{
 		$return = substr_compare($string, $start, 0, strlen($start)) === 0;
 
@@ -386,7 +374,7 @@ class Strings
 	 * @param string $end
 	 * @return bool
 	 */
-	public static function endsWith(string $string, string $end)
+	public static function endsWith(string $string, string $end): string
 	{
 		$return = substr_compare($string, $end, -strlen($end)) === 0;
 
@@ -399,7 +387,7 @@ class Strings
 	 * @return string
 	 * @see https://daringfireball.net/2010/07/improved_regex_for_matching_urls
 	 */
-	public static function autoLinkRegEx()
+	public static function autoLinkRegEx(): string
 	{
 		return '@
 (?<![=\'\]"/])			# Not preceded by [, =, \', ], ", /
@@ -429,7 +417,7 @@ class Strings
 	 * @param string $pathItem
 	 * @return string
 	 */
-	public static function sanitizeFilePathItem($pathItem)
+	public static function sanitizeFilePathItem(string $pathItem): string
 	{
 		$pathItem = str_replace('/', '_', $pathItem);
 		$pathItem = str_replace('\\', '_', $pathItem);
@@ -451,7 +439,7 @@ class Strings
 	 * @return string
 	 * @see substr_replace()
 	 */
-	public static function substringReplace(string $string, string $replacement, int $start, int $length = null)
+	public static function substringReplace(string $string, string $replacement, int $start, int $length = null): string
 	{
 		$string_length = mb_strlen($string);
 
diff --git a/src/Util/XML.php b/src/Util/XML.php
index f00cb7894..734fd9298 100644
--- a/src/Util/XML.php
+++ b/src/Util/XML.php
@@ -21,6 +21,9 @@
 
 namespace Friendica\Util;
 
+use DOMDocument;
+use DOMElement;
+use DOMNode;
 use DOMXPath;
 use Friendica\Core\Logger;
 use Friendica\Core\System;
@@ -39,22 +42,21 @@ class XML
 	 * @param bool   $remove_header Should the XML header be removed or not?
 	 * @param array  $namespaces    List of namespaces
 	 * @param bool   $root          interally used parameter. Mustn't be used from outside.
-	 *
-	 * @return string The created XML
+	 * @return void
 	 */
-	public static function fromArray($array, &$xml, $remove_header = false, $namespaces = [], $root = true)
+	public static function fromArray(array $array, &$xml, bool $remove_header = false, array $namespaces = [], bool $root = true)
 	{
 		if ($root) {
 			foreach ($array as $key => $value) {
 				foreach ($namespaces as $nskey => $nsvalue) {
-					$key .= " xmlns".($nskey == "" ? "":":").$nskey.'="'.$nsvalue.'"';
+					$key .= ' xmlns' . ($nskey == '' ? '' : ':') . $nskey . '="' . $nsvalue . '"';
 				}
 
 				if (is_array($value)) {
-					$root = new SimpleXMLElement("<".$key."/>");
+					$root = new SimpleXMLElement('<' . $key . '/>');
 					self::fromArray($value, $root, $remove_header, $namespaces, false);
 				} else {
-					$root = new SimpleXMLElement("<".$key.">".self::escape($value)."</".$key.">");
+					$root = new SimpleXMLElement('<' . $key . '>' . self::escape($value ?? '') . '</' . $key . '>');
 				}
 
 				$dom = dom_import_simplexml($root)->ownerDocument;
@@ -88,11 +90,11 @@ class XML
 				continue;
 			}
 
-			$element_parts = explode(":", $key);
+			$element_parts = explode(':', $key);
 			if ((count($element_parts) > 1) && isset($namespaces[$element_parts[0]])) {
 				$namespace = $namespaces[$element_parts[0]];
-			} elseif (isset($namespaces[""])) {
-				$namespace = $namespaces[""];
+			} elseif (isset($namespaces[''])) {
+				$namespace = $namespaces[''];
 			} else {
 				$namespace = null;
 			}
@@ -102,13 +104,13 @@ class XML
 				$key = $element_parts[1];
 			}
 
-			if (substr($key, 0, 11) == "@attributes") {
+			if (substr($key, 0, 11) == '@attributes') {
 				if (!isset($element) || !is_array($value)) {
 					continue;
 				}
 
 				foreach ($value as $attr_key => $attr_value) {
-					$element_parts = explode(":", $attr_key);
+					$element_parts = explode(':', $attr_key);
 					if ((count($element_parts) > 1) && isset($namespaces[$element_parts[0]])) {
 						$namespace = $namespaces[$element_parts[0]];
 					} else {
@@ -122,7 +124,7 @@ class XML
 			}
 
 			if (!is_array($value)) {
-				$element = $xml->addChild($key, self::escape($value), $namespace);
+				$element = $xml->addChild($key, self::escape($value ?? ''), $namespace);
 			} elseif (is_array($value)) {
 				$element = $xml->addChild($key, null, $namespace);
 				self::fromArray($value, $element, $remove_header, $namespaces, false);
@@ -138,7 +140,7 @@ class XML
 	 * @param string $elementname Name of the XML element of the target
 	 * @return void
 	 */
-	public static function copy(&$source, &$target, $elementname)
+	public static function copy(&$source, &$target, string $elementname)
 	{
 		if (count($source->children()) == 0) {
 			$target->addChild($elementname, self::escape($source));
@@ -153,14 +155,14 @@ class XML
 	/**
 	 * Create an XML element
 	 *
-	 * @param \DOMDocument $doc        XML root
+	 * @param DOMDocument $doc        XML root
 	 * @param string       $element    XML element name
 	 * @param string       $value      XML value
 	 * @param array        $attributes array containing the attributes
 	 *
 	 * @return \DOMElement XML element object
 	 */
-	public static function createElement(\DOMDocument $doc, $element, $value = "", $attributes = [])
+	public static function createElement(DOMDocument $doc, string $element, string $value = '', array $attributes = []): DOMElement
 	{
 		$element = $doc->createElement($element, self::escape($value));
 
@@ -175,14 +177,14 @@ class XML
 	/**
 	 * Create an XML and append it to the parent object
 	 *
-	 * @param \DOMDocument $doc        XML root
+	 * @param DOMDocument $doc        XML root
 	 * @param object $parent     parent object
 	 * @param string $element    XML element name
 	 * @param string $value      XML value
 	 * @param array  $attributes array containing the attributes
 	 * @return void
 	 */
-	public static function addElement(\DOMDocument $doc, $parent, $element, $value = "", $attributes = [])
+	public static function addElement(DOMDocument $doc, $parent, string $element, string $value = '', array $attributes = [])
 	{
 		$element = self::createElement($doc, $element, $value, $attributes);
 		$parent->appendChild($element);
@@ -198,7 +200,7 @@ class XML
 	 *
 	 * @return array | string The array from the xml element or the string
 	 */
-	public static function elementToArray($xml_element, &$recursion_depth = 0)
+	public static function elementToArray($xml_element, int &$recursion_depth = 0)
 	{
 		// If we're getting too deep, bail out
 		if ($recursion_depth > 512) {
@@ -217,7 +219,7 @@ class XML
 		if (is_array($xml_element)) {
 			$result_array = [];
 			if (count($xml_element) <= 0) {
-				return (trim(strval($xml_element_copy)));
+				return trim(strval($xml_element_copy));
 			}
 
 			foreach ($xml_element as $key => $value) {
@@ -233,9 +235,9 @@ class XML
 				];
 			}
 
-			return ($result_array);
+			return $result_array;
 		} else {
-			return (trim(strval($xml_element)));
+			return trim(strval($xml_element));
 		}
 	}
 
@@ -261,7 +263,7 @@ class XML
 	 * @return array The parsed XML in an array form. Use print_r() to see the resulting array structure.
 	 * @throws \Exception
 	 */
-	public static function toArray($contents, $namespaces = true, $get_attributes = 1, $priority = 'attribute')
+	public static function toArray(string $contents, bool $namespaces = true, int $get_attributes = 1, string $priority = 'attribute'): array
 	{
 		if (!$contents) {
 			return [];
@@ -300,7 +302,7 @@ class XML
 				Logger::debug('libxml: parse: ' . $err->code . " at " . $err->line . ":" . $err->column . " : " . $err->message);
 			}
 			libxml_clear_errors();
-			return;
+			return [];
 		}
 
 		//Initializations
@@ -414,20 +416,20 @@ class XML
 			}
 		}
 
-		return($xml_array);
+		return $xml_array;
 	}
 
 	/**
 	 * Delete a node in a XML object
 	 *
-	 * @param \DOMDocument $doc  XML document
+	 * @param DOMDocument $doc  XML document
 	 * @param string $node Node name
 	 * @return void
 	 */
-	public static function deleteNode(\DOMDocument $doc, $node)
+	public static function deleteNode(DOMDocument $doc, string $node)
 	{
 		$xpath = new DOMXPath($doc);
-		$list = $xpath->query("//".$node);
+		$list = $xpath->query('//' . $node);
 		foreach ($list as $child) {
 			$child->parentNode->removeChild($child);
 		}
@@ -436,9 +438,9 @@ class XML
 	/**
 	 * Parse XML string
 	 *
-	 * @param string  $s
-	 * @param boolean $suppress_log
-	 * @return Object
+	 * @param string  $s XML string to parse into object
+	 * @param boolean $suppress_log Whether to supressing logging
+	 * @return SimpleXMLElement|bool SimpleXMLElement or false on failure
 	 */
 	public static function parseString(string $s, bool $suppress_log = false)
 	{
@@ -458,7 +460,15 @@ class XML
 		return $x;
 	}
 
-	public static function getFirstNodeValue(DOMXPath $xpath, $element, $context = null)
+	/**
+	 * Gets first node value
+	 *
+	 * @param DOMXPath $xpath XPath object
+	 * @param string $element Element name
+	 * @param DOMNode $context Context object or NULL
+	 * @return string XML node value or empty string on failure
+	 */
+	public static function getFirstNodeValue(DOMXPath $xpath, string $element, DOMNode $context = null)
 	{
 		$result = @$xpath->evaluate($element, $context);
 		if (!is_object($result)) {
@@ -473,7 +483,15 @@ class XML
 		return $first_item->nodeValue;
 	}
 
-	public static function getFirstAttributes(DOMXPath $xpath, $element, $context = null)
+	/**
+	 * Gets first attributes
+	 *
+	 * @param DOMXPath $xpath XPath object
+	 * @param string $element Element name
+	 * @param DOMNode $context Context object or NULL
+	 * @return ???|bool First element's attributes field or false on failure
+	 */
+	public static function getFirstAttributes(DOMXPath $xpath, string $element, DOMNode $context = null)
 	{
 		$result = @$xpath->query($element, $context);
 		if (!is_object($result)) {
@@ -488,9 +506,17 @@ class XML
 		return $first_item->attributes;
 	}
 
-	public static function getFirstValue($xpath, $search, $context)
+	/**
+	 * Gets first node's value
+	 *
+	 * @param DOMXPath $xpath XPath object
+	 * @param string $element Element name
+	 * @param DOMNode $context Context object or NULL
+	 * @return string First value or empty string on failure
+	 */
+	public static function getFirstValue(DOMXPath $xpath, string $element, DOMNode $context = null): string
 	{
-		$result = @$xpath->query($search, $context);
+		$result = @$xpath->query($element, $context);
 		if (!is_object($result)) {
 			return '';
 		}
@@ -508,32 +534,31 @@ class XML
 	 *
 	 * @param string $str
 	 * @return string Escaped text.
+	 * @todo Move this generic method to Util\Strings and also rewrite all other findingd
 	 */
-	public static function escape($str)
+	public static function escape(string $str): string
 	{
-		$buffer = htmlspecialchars($str, ENT_QUOTES, 'UTF-8');
-		$buffer = trim($buffer);
-
-		return $buffer;
+		return trim(htmlspecialchars($str, ENT_QUOTES, 'UTF-8'));
 	}
 
 	/**
-	 * undo an escape
+	 * Undo an escape
 	 *
 	 * @param string $s xml escaped text
 	 * @return string unescaped text
+	 * @todo Move this generic method to Util\Strings and also rewrite all other findingd
 	 */
-	public static function unescape($s)
+	public static function unescape(string $s): string
 	{
-		$ret = htmlspecialchars_decode($s, ENT_QUOTES);
-		return $ret;
+		return htmlspecialchars_decode($s, ENT_QUOTES);
 	}
 
 	/**
-	 * apply escape() to all values of array $val, recursively
+	 * Apply escape() to all values of array $val, recursively
 	 *
-	 * @param array $val
-	 * @return array|string
+	 * @param array|bool|string $val Value of type bool, array or string
+	 * @return array|string Returns array if array provided or string in other cases
+	 * @todo Move this generic method to Util\Strings
 	 */
 	public static function arrayEscape($val)
 	{
diff --git a/src/Worker/Notifier.php b/src/Worker/Notifier.php
index 2039448e1..8c0801c66 100644
--- a/src/Worker/Notifier.php
+++ b/src/Worker/Notifier.php
@@ -81,7 +81,7 @@ class Notifier
 			$uid = $message['uid'];
 			$recipients[] = $message['contact-id'];
 
-			$mail = ActivityPub\Transmitter::ItemArrayFromMail($target_id);
+			$mail = ActivityPub\Transmitter::getItemArrayFromMail($target_id);
 			$inboxes = ActivityPub\Transmitter::fetchTargetInboxes($mail, $uid, true);
 			foreach ($inboxes as $inbox => $receivers) {
 				$ap_contacts = array_merge($ap_contacts, $receivers);
diff --git a/tests/Util/Database/ExtendedPDO.php b/tests/Util/Database/ExtendedPDO.php
index b127e312c..b36c126d5 100644
--- a/tests/Util/Database/ExtendedPDO.php
+++ b/tests/Util/Database/ExtendedPDO.php
@@ -33,7 +33,7 @@ class ExtendedPDO extends PDO
 	/**
 	 * @var array Database drivers that support SAVEPOINT * statements.
 	 */
-	protected static $_supportedDrivers = ["pgsql", "mysql"];
+	protected static $_supportedDrivers = ['pgsql', 'mysql'];
 
 	/**
 	 * @var int the current transaction depth
@@ -80,9 +80,9 @@ class ExtendedPDO extends PDO
 	/**
 	 * Commit current transaction
 	 *
-	 * @return bool|void
+	 * @return bool
 	 */
-	public function commit()
+	public function commit(): bool
 	{
 		// We don't want to "really" commit something, so skip the most outer hierarchy
 		if ($this->_transactionDepth <= 1 && $this->hasSavepoint()) {
@@ -92,28 +92,29 @@ class ExtendedPDO extends PDO
 
 		$this->_transactionDepth--;
 
-		$this->exec("RELEASE SAVEPOINT LEVEL{$this->_transactionDepth}");
+		return $this->exec("RELEASE SAVEPOINT LEVEL{$this->_transactionDepth}");
 	}
 
 	/**
 	 * Rollback current transaction,
 	 *
 	 * @throws PDOException if there is no transaction started
-	 * @return bool|void
+	 * @return bool Whether rollback was successful
 	 */
-	public function rollBack()
+	public function rollback(): bool
 	{
 		$this->_transactionDepth--;
 
-		if($this->_transactionDepth <= 0 || !$this->hasSavepoint()) {
+		if ($this->_transactionDepth <= 0 || !$this->hasSavepoint()) {
 			$this->_transactionDepth = 0;
 			try {
-				parent::rollBack();
+				return parent::rollBack();
 			} catch (PDOException $e) {
 				// this shouldn't happen, but it does ...
 			}
 		} else {
-			$this->exec("ROLLBACK TO SAVEPOINT LEVEL{$this->_transactionDepth}");
+			return $this->exec("ROLLBACK TO SAVEPOINT LEVEL{$this->_transactionDepth}");
 		}
+		return false;
 	}
 }
diff --git a/tests/Util/Database/StaticDatabase.php b/tests/Util/Database/StaticDatabase.php
index a6b2575f5..0782a9745 100644
--- a/tests/Util/Database/StaticDatabase.php
+++ b/tests/Util/Database/StaticDatabase.php
@@ -47,7 +47,7 @@ class StaticDatabase extends Database
 	 *
 	 * @return bool|void
 	 */
-	public function connect()
+	public function connect(): bool
 	{
 		if (!is_null($this->connection) && $this->connected()) {
 			return true;
@@ -81,7 +81,7 @@ class StaticDatabase extends Database
 	}
 
 	/** Mock for locking tables */
-	public function lock($table)
+	public function lock($table): bool
 	{
 		if ($this->_locked) {
 			return false;
@@ -94,7 +94,7 @@ class StaticDatabase extends Database
 	}
 
 	/** Mock for unlocking tables */
-	public function unlock()
+	public function unlock(): bool
 	{
 		// See here: https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html
 		$this->performCommit();
@@ -110,7 +110,7 @@ class StaticDatabase extends Database
 	 *
 	 * @return bool Was the command executed successfully?
 	 */
-	public function commit()
+	public function commit(): bool
 	{
 		if (!$this->performCommit()) {
 			return false;
diff --git a/tests/src/Database/DBATest.php b/tests/src/Database/DBATest.php
index c92133ac5..febe9c8c6 100644
--- a/tests/src/Database/DBATest.php
+++ b/tests/src/Database/DBATest.php
@@ -55,9 +55,6 @@ class DBATest extends DatabaseTest
 		self::assertTrue(DBA::exists('config', []));
 		self::assertFalse(DBA::exists('notable', []));
 
-		self::assertTrue(DBA::exists('config', null));
-		self::assertFalse(DBA::exists('notable', null));
-
 		self::assertTrue(DBA::exists('config', ['k' => 'hostname']));
 		self::assertFalse(DBA::exists('config', ['k' => 'nonsense']));
 	}
diff --git a/tests/src/Database/DBStructureTest.php b/tests/src/Database/DBStructureTest.php
index 638a98ed7..613e2f783 100644
--- a/tests/src/Database/DBStructureTest.php
+++ b/tests/src/Database/DBStructureTest.php
@@ -45,7 +45,6 @@ class DBStructureTest extends DatabaseTest
 	 */
 	public function testExists() {
 		self::assertTrue(DBStructure::existsTable('config'));
-
 		self::assertFalse(DBStructure::existsTable('notatable'));
 
 		self::assertTrue(DBStructure::existsColumn('config', ['k']));
diff --git a/tests/src/Util/StringsTest.php b/tests/src/Util/StringsTest.php
index 6f0fc32fe..830f97b2f 100644
--- a/tests/src/Util/StringsTest.php
+++ b/tests/src/Util/StringsTest.php
@@ -113,22 +113,18 @@ class StringsTest extends TestCase
 				'input' => '',
 				'valid' => false,
 			],
-			'nullHex' => [
-				'input' => null,
-				'valid' => false,
-			],
 		];
 	}
 
 	/**
 	 * Tests if the string is a valid hexadecimal value
 	 *
-	 * @param string|null $input
-	 * @param bool        $valid
+	 * @param string $input Input string
+	 * @param bool   $valid Whether testing on valid or invalid
 	 *
 	 * @dataProvider dataIsHex
 	 */
-	public function testIsHex(string $input = null, bool $valid = false)
+	public function testIsHex(string $input, bool $valid = false)
 	{
 		self::assertEquals($valid, Strings::isHex($input));
 	}
diff --git a/view/theme/frio/style.php b/view/theme/frio/style.php
index b39cef102..6d7e7b73f 100644
--- a/view/theme/frio/style.php
+++ b/view/theme/frio/style.php
@@ -79,7 +79,7 @@ if (!empty($_REQUEST['scheme'])) {
 	$scheme = $_REQUEST['scheme'];
 }
 
-$scheme = Strings::sanitizeFilePathItem($scheme);
+$scheme = Strings::sanitizeFilePathItem($scheme ?? '');
 
 if (($scheme) && ($scheme != '---')) {
 	if (file_exists('view/theme/frio/scheme/' . $scheme . '.php')) {