Explicitly cast Url objects to string

- Some systems do not do this operation automatically and it results in empty DB fields

src/Navigation/Notifications/Depository/Notify.php

@@ -104,11 +104,11 @@ class Notify extends BaseDepository
 		$fields = [
 			'type'          => $Notify->type,
 			'name'          => $Notify->name,
-			'url'           => $Notify->url,
-			'photo'         => $Notify->photo,
+			'url'           => (string)$Notify->url,
+			'photo'         => (string)$Notify->photo,
 			'msg'           => $Notify->msg,
 			'uid'           => $Notify->uid,
-			'link'          => $Notify->link,
+			'link'          => (string)$Notify->link,
 			'iid'           => $Notify->itemId,
 			'parent'        => $Notify->parent,
 			'seen'          => $Notify->seen,