Initial annotations/nullability changes (#3392)

src/main/java/net/minecraftforge/client/event/RenderItemInFrameEvent.java

@@ -25,6 +25,8 @@ import net.minecraft.item.ItemStack;
 import net.minecraftforge.fml.common.eventhandler.Cancelable;
 import net.minecraftforge.fml.common.eventhandler.Event;
 
+import javax.annotation.Nonnull;
+
 /**
  * This event is called when an item is rendered in an item frame.
  * 
@@ -44,6 +46,7 @@ public class RenderItemInFrameEvent extends Event
         renderer = renderItemFrame;
     }
 
+    @Nonnull
     public ItemStack getItem()
     {
         return item;

src/main/java/net/minecraftforge/client/event/RenderSpecificHandEvent.java

@@ -5,6 +5,7 @@ import net.minecraft.util.EnumHand;
 import net.minecraftforge.fml.common.eventhandler.Cancelable;
 import net.minecraftforge.fml.common.eventhandler.Event;
 
+import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 /**
@@ -23,7 +24,7 @@ public class RenderSpecificHandEvent extends Event
     private final float equipProgress;
     private final ItemStack stack;
 
-    public RenderSpecificHandEvent(EnumHand hand, float partialTicks, float interpolatedPitch, float swingProgress, float equipProgress, ItemStack stack)
+    public RenderSpecificHandEvent(EnumHand hand, float partialTicks, float interpolatedPitch, float swingProgress, float equipProgress, @Nonnull ItemStack stack)
     {
         this.hand = hand;
         this.partialTicks = partialTicks;
@@ -70,7 +71,7 @@ public class RenderSpecificHandEvent extends Event
     /**
      * @return The ItemStack to be rendered, or null.
      */
-    @Nullable
+    @Nonnull
     public ItemStack getItemStack()
     {
         return stack;

src/main/java/net/minecraftforge/client/event/RenderTooltipEvent.java

@@ -32,7 +32,7 @@ public abstract class RenderTooltipEvent extends Event
     protected int y;
     protected FontRenderer fr;
 
-    public RenderTooltipEvent(@Nullable ItemStack stack, @Nonnull List<String> lines, int x, int y, @Nonnull FontRenderer fr)
+    public RenderTooltipEvent(@Nonnull ItemStack stack, @Nonnull List<String> lines, int x, int y, @Nonnull FontRenderer fr)
     {
         this.stack = stack;
         this.lines = Collections.unmodifiableList(lines); // Leave editing to ItemTooltipEvent
@@ -44,7 +44,7 @@ public abstract class RenderTooltipEvent extends Event
     /**
      * @return The stack which the tooltip is being rendered for. As tooltips can be drawn without itemstacks, this return is {@link Nullable}. 
      */
-    @Nullable
+    @Nonnull
     public ItemStack getStack()
     {
         return stack;

src/main/java/net/minecraftforge/common/ForgeHooks.java

@@ -142,6 +142,7 @@ public class ForgeHooks
     }
     static final List<SeedEntry> seedList = new ArrayList<SeedEntry>();
 
+    @Nonnull
     public static ItemStack getGrassSeed(Random rand, int fortune)
     {
         SeedEntry entry = WeightedRandom.getRandomItem(rand, seedList);
@@ -207,7 +208,7 @@ public class ForgeHooks
         }
     }
 
-    public static boolean isToolEffective(IBlockAccess world, BlockPos pos, ItemStack stack)
+    public static boolean isToolEffective(IBlockAccess world, BlockPos pos, @Nonnull ItemStack stack)
     {
         IBlockState state = world.getBlockState(pos);
         state = state.getBlock().getActualState(state, world, pos);
@@ -792,7 +793,7 @@ public class ForgeHooks
         return event.isCanceled() ? -1 : event.getExpToDrop();
     }
 
-    public static EnumActionResult onPlaceItemIntoWorld(ItemStack itemstack, EntityPlayer player, World world, BlockPos pos, EnumFacing side, float hitX, float hitY, float hitZ, EnumHand hand)
+    public static EnumActionResult onPlaceItemIntoWorld(@Nonnull  ItemStack itemstack, EntityPlayer player, World world, BlockPos pos, EnumFacing side, float hitX, float hitY, float hitZ, EnumHand hand)
     {
         // handle all placement events here
         int meta = itemstack.getItemDamage();
@@ -883,7 +884,7 @@ public class ForgeHooks
         return ret;
     }
 
-    public static boolean onAnvilChange(ContainerRepair container, ItemStack left, ItemStack right, IInventory outputSlot, String name, int baseCost)
+    public static boolean onAnvilChange(ContainerRepair container, @Nonnull ItemStack left, @Nonnull ItemStack right, IInventory outputSlot, String name, int baseCost)
     {
         AnvilUpdateEvent e = new AnvilUpdateEvent(left, right, name, baseCost);
         if (MinecraftForge.EVENT_BUS.post(e)) return false;
@@ -1061,7 +1062,7 @@ public class ForgeHooks
         MinecraftForge.EVENT_BUS.post(new PlayerInteractEvent.RightClickEmpty(player, hand));
     }
 
-    public static void onEmptyLeftClick(EntityPlayer player, ItemStack stack)
+    public static void onEmptyLeftClick(EntityPlayer player, @Nonnull ItemStack stack)
     {
         MinecraftForge.EVENT_BUS.post(new PlayerInteractEvent.LeftClickEmpty(player, stack));
     }

src/main/java/net/minecraftforge/common/IShearable.java

@@ -25,6 +25,8 @@ import net.minecraft.item.ItemStack;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockAccess;
 
+import javax.annotation.Nonnull;
+
 /**
  *
  * This allows for mods to create there own Shear-like items
@@ -44,7 +46,7 @@ public interface IShearable
      * @param pos Block's position in world.
      * @return If this is shearable, and onSheared should be called.
      */
-    public boolean isShearable(ItemStack item, IBlockAccess world, BlockPos pos);
+    public boolean isShearable(@Nonnull ItemStack item, IBlockAccess world, BlockPos pos);
 
     /**
      * Performs the shear function on this object.
@@ -64,5 +66,5 @@ public interface IShearable
      * @param fortune The fortune level of the shears being used
      * @return A ArrayList containing all items from this shearing. Possible to be null.
      */
-    public List<ItemStack> onSheared(ItemStack item, IBlockAccess world, BlockPos pos, int fortune);
+    public List<ItemStack> onSheared(@Nonnull ItemStack item, IBlockAccess world, BlockPos pos, int fortune);
 }

src/main/java/net/minecraftforge/common/ISpecialArmor.java

@@ -34,6 +34,8 @@ import net.minecraft.item.ItemArmor;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.NonNullList;
 
+import javax.annotation.Nonnull;
+
 /**
  * This interface is to be implemented by ItemArmor classes. It will allow to
  * modify computation of damage and health loss. Computation will be called
@@ -60,7 +62,7 @@ public interface ISpecialArmor
      * @param slot The armor slot the item is in.
      * @return A ArmorProperties instance holding information about how the armor effects damage.
      */
-    public ArmorProperties getProperties(EntityLivingBase player, ItemStack armor, DamageSource source, double damage, int slot);
+    public ArmorProperties getProperties(EntityLivingBase player, @Nonnull ItemStack armor, DamageSource source, double damage, int slot);
 
     /**
      * Get the displayed effective armor.
@@ -70,7 +72,7 @@ public interface ISpecialArmor
      * @param slot The armor slot the item is in.
      * @return The number of armor points for display, 2 per shield.
      */
-    public abstract int getArmorDisplay(EntityPlayer player, ItemStack armor, int slot);
+    public abstract int getArmorDisplay(EntityPlayer player, @Nonnull ItemStack armor, int slot);
 
     /**
      * Applies damage to the ItemStack. The mod is responsible for reducing the
@@ -84,7 +86,7 @@ public interface ISpecialArmor
      * @param damage The amount of damage being applied to the armor
      * @param slot The armor slot the item is in.
      */
-    public abstract void damageArmor(EntityLivingBase entity, ItemStack stack, DamageSource source, int damage, int slot);
+    public abstract void damageArmor(EntityLivingBase entity, @Nonnull ItemStack stack, DamageSource source, int damage, int slot);
 
     public static class ArmorProperties implements Comparable<ArmorProperties>
     {

src/main/java/net/minecraftforge/common/MinecraftForge.java

@@ -41,6 +41,8 @@ import net.minecraftforge.common.ForgeHooks.SeedEntry;
 import net.minecraftforge.fluids.FluidRegistry;
 import net.minecraftforge.oredict.OreDictionary;
 
+import javax.annotation.Nonnull;
+
 public class MinecraftForge
 {
     /**
@@ -67,7 +69,7 @@ public class MinecraftForge
      *
      * Note: These functions may be going away soon, we're looking into loot tables....
      */
-    public static void addGrassSeed(ItemStack seed, int weight)
+    public static void addGrassSeed(@Nonnull ItemStack seed, int weight)
     {
         addGrassSeed(new SeedEntry(seed, weight));
     }

src/main/java/net/minecraftforge/common/brewing/AbstractBrewingRecipe.java

@@ -22,23 +22,20 @@ package net.minecraftforge.common.brewing;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.oredict.OreDictionary;
 
+import javax.annotation.Nonnull;
+
 public abstract class AbstractBrewingRecipe<T> implements IBrewingRecipe {
 
     private final ItemStack input;
     private final T ingredient;
     private final ItemStack output;
 
-    protected AbstractBrewingRecipe(ItemStack input, T ingredient, ItemStack output)
+    protected AbstractBrewingRecipe(@Nonnull ItemStack input, @Nonnull T ingredient, @Nonnull ItemStack output)
     {
         this.input = input;
         this.ingredient = ingredient;
         this.output = output;
 
-        if (this.getInput() == null || this.getIngredient() == null || this.getOutput() == null)
-        {
-            throw new IllegalArgumentException("A brewing recipe cannot have a null parameter.");
-        }
-        
         if (this.getInput().getMaxStackSize() != 1)
         {
             throw new IllegalArgumentException("Inputs must have a max size of 1 just like water bottles. Brewing Stands override the input with the output when the brewing is done, items that stack would end up getting lost.");
@@ -46,27 +43,31 @@ public abstract class AbstractBrewingRecipe<T> implements IBrewingRecipe {
     }
 
     @Override
-    public boolean isInput(ItemStack stack)
+    public boolean isInput(@Nonnull ItemStack stack)
     {
         return OreDictionary.itemMatches(this.getInput(), stack, false);
     }
 
     @Override
-    public ItemStack getOutput(ItemStack input, ItemStack ingredient)
+    @Nonnull
+    public ItemStack getOutput(@Nonnull ItemStack input, @Nonnull ItemStack ingredient)
     {
-        return isInput(input) && isIngredient(ingredient) ? getOutput().copy() : null;
+        return isInput(input) && isIngredient(ingredient) ? getOutput().copy() : ItemStack.field_190927_a;
     }
 
+    @Nonnull
     public ItemStack getInput()
     {
         return input;
     }
 
+    @Nonnull
     public T getIngredient()
     {
         return ingredient;
     }
 
+    @Nonnull
     public ItemStack getOutput()
     {
         return output;

src/main/java/net/minecraftforge/common/brewing/BrewingOreRecipe.java

@@ -23,20 +23,22 @@ import java.util.List;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.oredict.OreDictionary;
 
+import javax.annotation.Nonnull;
+
 public class BrewingOreRecipe extends AbstractBrewingRecipe<List<ItemStack>> {
 
-    public BrewingOreRecipe(ItemStack input, String ingredient, ItemStack output)
+    public BrewingOreRecipe(@Nonnull ItemStack input, @Nonnull String ingredient, @Nonnull ItemStack output)
     {
         super(input, OreDictionary.getOres(ingredient), output);
     }
 
-    public BrewingOreRecipe(ItemStack input, List<ItemStack> ingredient, ItemStack output)
+    public BrewingOreRecipe(@Nonnull ItemStack input, @Nonnull List<ItemStack> ingredient, @Nonnull ItemStack output)
     {
         super(input, ingredient, output);
     }
 
     @Override
-    public boolean isIngredient(ItemStack stack)
+    public boolean isIngredient(@Nonnull ItemStack stack)
     {
         for (ItemStack target : this.getIngredient())
         {

src/main/java/net/minecraftforge/common/brewing/BrewingRecipe.java

@@ -22,15 +22,17 @@ package net.minecraftforge.common.brewing;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.oredict.OreDictionary;
 
+import javax.annotation.Nonnull;
+
 public class BrewingRecipe extends AbstractBrewingRecipe<ItemStack> {
 
-    public BrewingRecipe(ItemStack input, ItemStack ingredient, ItemStack output)
+    public BrewingRecipe(@Nonnull ItemStack input, @Nonnull ItemStack ingredient, @Nonnull ItemStack output)
     {
         super(input, ingredient, output);
     }
 
     @Override
-    public boolean isIngredient(ItemStack stack)
+    public boolean isIngredient(@Nonnull ItemStack stack)
     {
         return OreDictionary.itemMatches(this.getIngredient(), stack, false);
     }

src/main/java/net/minecraftforge/common/brewing/BrewingRecipeRegistry.java

@@ -50,7 +50,7 @@ public class BrewingRecipeRegistry {
      *            done.
      * @return true if the recipe was added.
      */
-    public static boolean addRecipe(ItemStack input, ItemStack ingredient, ItemStack output)
+    public static boolean addRecipe(@Nonnull ItemStack input, @Nonnull ItemStack ingredient, @Nonnull ItemStack output)
     {
         return addRecipe(new BrewingRecipe(input, ingredient, output));
     }
@@ -69,7 +69,7 @@ public class BrewingRecipeRegistry {
      *            done.
      * @return true if the recipe was added.
      */
-    public static boolean addRecipe(ItemStack input, String ingredient, ItemStack output)
+    public static boolean addRecipe(@Nonnull ItemStack input, @Nonnull String ingredient, @Nonnull ItemStack output)
     {
         return addRecipe(new BrewingOreRecipe(input, ingredient, output));
     }
@@ -85,10 +85,10 @@ public class BrewingRecipeRegistry {
 
     /**
      * Returns the output ItemStack obtained by brewing the passed input and
-     * ingredient. Null if no matches are found.
+     * ingredient.
      */
     @Nonnull
-    public static ItemStack getOutput(@Nonnull ItemStack input, ItemStack ingredient)
+    public static ItemStack getOutput(@Nonnull ItemStack input, @Nonnull ItemStack ingredient)
     {
         if (input.func_190926_b() || input.getMaxStackSize() != 1 || input.func_190916_E() != 1) return ItemStack.field_190927_a;
         if (ingredient.func_190926_b()) return ItemStack.field_190927_a;
@@ -107,7 +107,7 @@ public class BrewingRecipeRegistry {
     /**
      * Returns true if the passed input and ingredient have an output
      */
-    public static boolean hasOutput(ItemStack input, ItemStack ingredient)
+    public static boolean hasOutput(@Nonnull ItemStack input, @Nonnull ItemStack ingredient)
     {
         return !getOutput(input, ingredient).func_190926_b();
     }

src/main/java/net/minecraftforge/common/brewing/IBrewingRecipe.java

@@ -21,6 +21,8 @@ package net.minecraftforge.common.brewing;
 
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public interface IBrewingRecipe {
 
     /**
@@ -28,18 +30,18 @@ public interface IBrewingRecipe {
      * being the item that goes in one of the three bottom slots of the brewing
      * stand (e.g: water bottle)
      */
-    public boolean isInput(ItemStack input);
+    public boolean isInput(@Nonnull ItemStack input);
 
     /**
      * Returns true if the passed ItemStack is an ingredient for this recipe.
      * "Ingredient" being the item that goes in the top slot of the brewing
      * stand (e.g: nether wart)
      */
-    public boolean isIngredient(ItemStack ingredient);
+    public boolean isIngredient(@Nonnull ItemStack ingredient);
 
     /**
      * Returns the output when the passed input is brewed with the passed
      * ingredient. Null if invalid input or ingredient.
      */
-    public ItemStack getOutput(ItemStack input, ItemStack ingredient);
+    public ItemStack getOutput(@Nonnull ItemStack input, @Nonnull ItemStack ingredient);
 }

src/main/java/net/minecraftforge/common/brewing/VanillaBrewingRecipe.java

@@ -24,6 +24,8 @@ import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.potion.PotionHelper;
 
+import javax.annotation.Nonnull;
+
 /**
  * Used in BrewingRecipeRegistry to maintain the vanilla behaviour.
  *
@@ -35,7 +37,7 @@ public class VanillaBrewingRecipe implements IBrewingRecipe {
      * Code adapted from TileEntityBrewingStand.isItemValidForSlot(int index, ItemStack stack)
      */
     @Override
-    public boolean isInput(ItemStack stack)
+    public boolean isInput(@Nonnull ItemStack stack)
     {
         Item item = stack.getItem();
         return item == Items.POTIONITEM || item == Items.SPLASH_POTION || item == Items.LINGERING_POTION || item == Items.GLASS_BOTTLE;
@@ -45,7 +47,7 @@ public class VanillaBrewingRecipe implements IBrewingRecipe {
      * Code adapted from TileEntityBrewingStand.isItemValidForSlot(int index, ItemStack stack)
      */
     @Override
-    public boolean isIngredient(ItemStack stack)
+    public boolean isIngredient(@Nonnull ItemStack stack)
     {
         return PotionHelper.isReagent(stack);
     }
@@ -56,18 +58,18 @@ public class VanillaBrewingRecipe implements IBrewingRecipe {
      * or if the new potion is a splash potion when the old one wasn't.
      */
     @Override
-    public ItemStack getOutput(ItemStack input, ItemStack ingredient)
+    public ItemStack getOutput(@Nonnull ItemStack input, @Nonnull ItemStack ingredient)
     {
-        if (ingredient != null && input != null && isIngredient(ingredient))
+        if (!input.func_190926_b() && !ingredient.func_190926_b() && isIngredient(ingredient))
         {
             ItemStack result = PotionHelper.doReaction(ingredient, input);
             if (result != input)
             {
                 return result;
             }
-            return null;
+            return ItemStack.field_190927_a;
         }
 
-        return null;
+        return ItemStack.field_190927_a;
     }
 }

src/main/java/net/minecraftforge/event/AttachCapabilitiesEvent.java

@@ -28,6 +28,8 @@ import net.minecraft.util.ResourceLocation;
 import net.minecraftforge.common.capabilities.ICapabilityProvider;
 import net.minecraftforge.fml.common.eventhandler.GenericEvent;
 
+import javax.annotation.Nonnull;
+
 /**
  * Fired whenever an object with Capabilities support {currently TileEntity/Item/Entity)
  * is created. Allowing for the attachment of arbitrary capability providers.
@@ -126,10 +128,10 @@ public class AttachCapabilitiesEvent<T> extends GenericEvent<T>
      */
     public static class Item extends AttachCapabilitiesEvent<net.minecraft.item.Item>
     {
-        @Deprecated
         private final net.minecraft.item.ItemStack stack;
+        @Deprecated
         private final net.minecraft.item.Item item;
-        public Item(net.minecraft.item.Item item, net.minecraft.item.ItemStack stack)
+        public Item(net.minecraft.item.Item item, @Nonnull  net.minecraft.item.ItemStack stack)
         {
             super(net.minecraft.item.Item.class, item);
             this.item = item;
@@ -140,6 +142,7 @@ public class AttachCapabilitiesEvent<T> extends GenericEvent<T>
         {
             return this.item;
         }
+        @Nonnull
         public net.minecraft.item.ItemStack getItemStack()
         {
             return this.stack;

src/main/java/net/minecraftforge/event/ForgeEventFactory.java

@@ -398,9 +398,9 @@ public class ForgeEventFactory
         return event;
     }
 
-    public static int onItemExpire(EntityItem entity, ItemStack item)
+    public static int onItemExpire(EntityItem entity, @Nonnull ItemStack item)
     {
-        if (item == null) return -1;
+        if (item.func_190926_b()) return -1;
         ItemExpireEvent event = new ItemExpireEvent(entity, (item.func_190926_b() ? 6000 : item.getItem().getEntityLifespan(item, entity.worldObj)));
         if (!MinecraftForge.EVENT_BUS.post(event)) return -1;
         return event.getExtraLife();

src/main/java/net/minecraftforge/event/brewing/PlayerBrewedPotionEvent.java

@@ -23,6 +23,8 @@ import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.event.entity.player.PlayerEvent;
 
+import javax.annotation.Nonnull;
+
 /**
  * This event is called when a player picks up a potion from a brewing stand.
  */
@@ -30,7 +32,7 @@ public class PlayerBrewedPotionEvent extends PlayerEvent
 {
     private final ItemStack stack;
 
-    public PlayerBrewedPotionEvent(EntityPlayer player, ItemStack stack)
+    public PlayerBrewedPotionEvent(EntityPlayer player, @Nonnull ItemStack stack)
     {
         super(player);
         this.stack = stack;
@@ -39,6 +41,7 @@ public class PlayerBrewedPotionEvent extends PlayerEvent
     /**
      * The ItemStack of the potion.
      */
+    @Nonnull
     public ItemStack getStack()
     {
         return stack;

src/main/java/net/minecraftforge/event/brewing/PotionBrewEvent.java

@@ -27,6 +27,8 @@ import net.minecraftforge.fml.common.eventhandler.Cancelable;
 import net.minecraftforge.fml.common.eventhandler.Event;
 import net.minecraftforge.fml.common.eventhandler.Event.HasResult;
 
+import javax.annotation.Nonnull;
+
 
 public class PotionBrewEvent extends Event
 {
@@ -37,13 +39,14 @@ public class PotionBrewEvent extends Event
         this.stacks = stacks;
     }
 
+    @Nonnull
     public ItemStack getItem(int index)
     {
-        if (index >= stacks.size()) return null;
+        if (index >= stacks.size()) return ItemStack.field_190927_a;
         return stacks.get(index);
     }
 
-    public void setItem(int index, ItemStack stack)
+    public void setItem(int index, @Nonnull ItemStack stack)
     {
         if (index < stacks.size())
         {

src/main/java/net/minecraftforge/event/entity/living/LivingEntityUseItemEvent.java

@@ -23,18 +23,21 @@ import net.minecraft.entity.EntityLivingBase;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.fml.common.eventhandler.Cancelable;
 
+import javax.annotation.Nonnull;
+
 public abstract class LivingEntityUseItemEvent extends LivingEvent
 {
     private final ItemStack item;
     private int duration;
 
-    private LivingEntityUseItemEvent(EntityLivingBase entity, ItemStack item, int duration)
+    private LivingEntityUseItemEvent(EntityLivingBase entity, @Nonnull ItemStack item, int duration)
     {
         super(entity);
         this.item = item;
         this.setDuration(duration);
     }
 
+    @Nonnull
     public ItemStack getItem()
     {
         return item;
@@ -64,7 +67,7 @@ public abstract class LivingEntityUseItemEvent extends LivingEvent
     @Cancelable
     public static class Start extends LivingEntityUseItemEvent
     {
-        public Start(EntityLivingBase entity, ItemStack item, int duration)
+        public Start(EntityLivingBase entity, @Nonnull ItemStack item, int duration)
         {
             super(entity, item, duration);
         }
@@ -79,7 +82,7 @@ public abstract class LivingEntityUseItemEvent extends LivingEvent
     @Cancelable
     public static class Tick extends LivingEntityUseItemEvent
     {
-        public Tick(EntityLivingBase entity, ItemStack item, int duration)
+        public Tick(EntityLivingBase entity, @Nonnull ItemStack item, int duration)
         {
             super(entity, item, duration);
         }
@@ -100,7 +103,7 @@ public abstract class LivingEntityUseItemEvent extends LivingEvent
     @Cancelable
     public static class Stop extends LivingEntityUseItemEvent
     {
-        public Stop(EntityLivingBase entity, ItemStack item, int duration)
+        public Stop(EntityLivingBase entity, @Nonnull ItemStack item, int duration)
         {
             super(entity, item, duration);
         }
@@ -119,18 +122,19 @@ public abstract class LivingEntityUseItemEvent extends LivingEvent
     public static class Finish extends LivingEntityUseItemEvent
     {
         private ItemStack result;
-        public Finish(EntityLivingBase entity, ItemStack item, int duration, ItemStack result)
+        public Finish(EntityLivingBase entity, @Nonnull ItemStack item, int duration, @Nonnull ItemStack result)
         {
             super(entity, item, duration);
             this.setResultStack(result);
         }
 
+        @Nonnull
         public ItemStack getResultStack()
         {
             return result;
         }
 
-        public void setResultStack(ItemStack result)
+        public void setResultStack(@Nonnull ItemStack result)
         {
             this.result = result;
         }

src/main/java/net/minecraftforge/event/entity/minecart/MinecartInteractEvent.java

@@ -30,6 +30,8 @@ import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.EnumHand;
 
+import javax.annotation.Nonnull;
+
 /**
  * MinecartInteractEvent is fired when a player interacts with a minecart. <br>
  * This event is fired whenever a player interacts with a minecart in
@@ -62,6 +64,7 @@ public class MinecartInteractEvent extends MinecartEvent
     }
 
     public EntityPlayer getPlayer() { return player; }
+    @Nonnull
     public ItemStack getItem() { return player.getHeldItem(hand); }
     public EnumHand getHand() { return hand; }
 }

src/main/java/net/minecraftforge/event/entity/player/AnvilRepairEvent.java

@@ -22,6 +22,8 @@ package net.minecraftforge.event.entity.player;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 /**
  * Fired when the player removes a "repaired" item from the Anvil's Output slot.
  *
@@ -37,7 +39,7 @@ public class AnvilRepairEvent extends PlayerEvent
     private final ItemStack output; // Set this to set the output stack
     private float breakChance; // Anvil's chance to break (reduced by 1 durability) when this is complete. Default is 12% (0.12f)
 
-    public AnvilRepairEvent(EntityPlayer player, ItemStack left, ItemStack right, ItemStack output)
+    public AnvilRepairEvent(EntityPlayer player, @Nonnull ItemStack left, @Nonnull ItemStack right, ItemStack output)
     {
         super(player);
         this.output = output;
@@ -69,18 +71,21 @@ public class AnvilRepairEvent extends PlayerEvent
      * Get the output result from the anvil
      * @return the output
      */
+    @Nonnull
     public ItemStack getItemResult() { return output; }
 
     /**
      * Get the first item input into the anvil
      * @return the first input slot
      */
+    @Nonnull
     public ItemStack getItemInput() { return left; }
 
     /**
      * Get the second item input into the anvil
      * @return the second input slot
      */
+    @Nonnull
     public ItemStack getIngredientInput() { return right; }
 
     public float getBreakChance() { return breakChance; }

src/main/java/net/minecraftforge/event/entity/player/ArrowLooseEvent.java

@@ -27,6 +27,8 @@ import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.ItemStack;
 import net.minecraft.world.World;
 
+import javax.annotation.Nonnull;
+
 /**
  * ArrowLooseEvent is fired when a player stops using a bow.<br>
  * This event is fired whenever a player stops using a bow in
@@ -50,7 +52,7 @@ public class ArrowLooseEvent extends PlayerEvent
     private final boolean hasAmmo;
     private int charge;
 
-    public ArrowLooseEvent(EntityPlayer player, ItemStack bow, World world, int charge, boolean hasAmmo)
+    public ArrowLooseEvent(EntityPlayer player, @Nonnull ItemStack bow, World world, int charge, boolean hasAmmo)
     {
         super(player);
         this.bow = bow;
@@ -59,6 +61,7 @@ public class ArrowLooseEvent extends PlayerEvent
         this.hasAmmo = hasAmmo;
     }
 
+    @Nonnull
     public ItemStack getBow() { return this.bow; }
     public World getWorld() { return this.world; }
     public boolean hasAmmo() { return this.hasAmmo; }

src/main/java/net/minecraftforge/event/entity/player/ArrowNockEvent.java

@@ -27,6 +27,8 @@ import net.minecraft.util.EnumHand;
 import net.minecraft.world.World;
 import net.minecraftforge.common.MinecraftForge;
 
+import javax.annotation.Nonnull;
+
 /**
  * ArrowNockEvent is fired when a player begins using a bow.<br>
  * This event is fired whenever a player begins using a bow in
@@ -42,7 +44,7 @@ public class ArrowNockEvent extends PlayerEvent
     private final boolean hasAmmo;
     private ActionResult<ItemStack> action;
 
-    public ArrowNockEvent(EntityPlayer player, ItemStack item, EnumHand hand, World world, boolean hasAmmo)
+    public ArrowNockEvent(EntityPlayer player, @Nonnull ItemStack item, EnumHand hand, World world, boolean hasAmmo)
     {
         super(player);
         this.bow = item;
@@ -51,6 +53,7 @@ public class ArrowNockEvent extends PlayerEvent
         this.hasAmmo = hasAmmo;
     }
 
+    @Nonnull
     public ItemStack getBow() { return this.bow; }
     public World getWorld() { return this.world; }
     public EnumHand getHand() { return this.hand; }

src/main/java/net/minecraftforge/event/entity/player/FillBucketEvent.java

@@ -26,6 +26,8 @@ import net.minecraft.item.ItemStack;
 import net.minecraft.util.math.RayTraceResult;
 import net.minecraft.world.World;
 
+import javax.annotation.Nonnull;
+
 /**
  * This event is fired when a player attempts to use a Empty bucket, it
  * can be canceled to completely prevent any further processing.
@@ -46,7 +48,7 @@ public class FillBucketEvent extends PlayerEvent
 
     private ItemStack result;
 
-    public FillBucketEvent(EntityPlayer player, ItemStack current, World world, RayTraceResult target)
+    public FillBucketEvent(EntityPlayer player, @Nonnull ItemStack current, World world, RayTraceResult target)
     {
         super(player);
         this.current = current;
@@ -54,9 +56,11 @@ public class FillBucketEvent extends PlayerEvent
         this.target = target;
     }
 
+    @Nonnull
     public ItemStack getEmptyBucket() { return this.current; }
     public World getWorld(){ return this.world; }
     public RayTraceResult getTarget() { return this.target; }
+    @Nonnull
     public ItemStack getFilledBucket() { return this.result; }
-    public void setFilledBucket(ItemStack bucket) { this.result = bucket; }
+    public void setFilledBucket(@Nonnull ItemStack bucket) { this.result = bucket; }
 }

src/main/java/net/minecraftforge/event/entity/player/ItemTooltipEvent.java

@@ -23,16 +23,19 @@ import java.util.List;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public class ItemTooltipEvent extends PlayerEvent
 {
     private final boolean showAdvancedItemTooltips;
+    @Nonnull
     private final ItemStack itemStack;
     private final List<String> toolTip;
 
     /**
      * This event is fired in {@link ItemStack#getTooltip(EntityPlayer, boolean)}, which in turn is called from it's respective GUIContainer.
      */
-    public ItemTooltipEvent(ItemStack itemStack, EntityPlayer entityPlayer, List<String> toolTip, boolean showAdvancedItemTooltips)
+    public ItemTooltipEvent(@Nonnull ItemStack itemStack, EntityPlayer entityPlayer, List<String> toolTip, boolean showAdvancedItemTooltips)
     {
         super(entityPlayer);
         this.itemStack = itemStack;
@@ -51,6 +54,7 @@ public class ItemTooltipEvent extends PlayerEvent
     /**
      * The {@link ItemStack} with the tooltip.
      */
+    @Nonnull
     public ItemStack getItemStack()
     {
         return itemStack;

src/main/java/net/minecraftforge/event/entity/player/PlayerInteractEvent.java

@@ -313,7 +313,7 @@ public class PlayerInteractEvent extends PlayerEvent
      */
     public static class LeftClickEmpty extends PlayerInteractEvent
     {
-        public LeftClickEmpty(EntityPlayer player, ItemStack stack)
+        public LeftClickEmpty(EntityPlayer player, @Nonnull ItemStack stack)
         {
             super(player, EnumHand.MAIN_HAND, new BlockPos(player), null);
         }

src/main/java/net/minecraftforge/event/entity/player/UseHoeEvent.java

@@ -26,6 +26,8 @@ import net.minecraft.world.World;
 import net.minecraftforge.fml.common.eventhandler.Cancelable;
 import net.minecraftforge.fml.common.eventhandler.Event;
 
+import javax.annotation.Nonnull;
+
 /**
  * This event is fired when a player attempts to use a Hoe on a block, it
  * can be canceled to completely prevent any further processing.
@@ -44,7 +46,7 @@ public class UseHoeEvent extends PlayerEvent
     private final World world;
     private final BlockPos pos;
 
-    public UseHoeEvent(EntityPlayer player, ItemStack current, World world, BlockPos pos)
+    public UseHoeEvent(EntityPlayer player, @Nonnull ItemStack current, World world, BlockPos pos)
     {
         super(player);
         this.current = current;
@@ -52,6 +54,7 @@ public class UseHoeEvent extends PlayerEvent
         this.pos = pos;
     }
 
+    @Nonnull
     public ItemStack getCurrent()
     {
         return current;

src/main/java/net/minecraftforge/fluids/DispenseFluidContainer.java

@@ -95,7 +95,8 @@ public class DispenseFluidContainer extends BehaviorDefaultDispenseItem
     /**
      * Drains a filled container and places the fluid in front of the Dispenser.
      */
-    private ItemStack dumpContainer(IBlockSource source, ItemStack stack)
+    @Nonnull
+    private ItemStack dumpContainer(IBlockSource source, @Nonnull ItemStack stack)
     {
         ItemStack singleStack = stack.copy();
         singleStack.func_190920_e(1);

src/main/java/net/minecraftforge/fluids/UniversalBucket.java

@@ -84,13 +84,14 @@ public class UniversalBucket extends Item
     }
 
     @Override
-    public boolean hasContainerItem(ItemStack stack)
+    public boolean hasContainerItem(@Nonnull ItemStack stack)
     {
         return !getEmpty().func_190926_b();
     }
 
+    @Nonnull
     @Override
-    public ItemStack getContainerItem(ItemStack itemStack)
+    public ItemStack getContainerItem(@Nonnull ItemStack itemStack)
     {
         if (!getEmpty().func_190926_b())
         {
@@ -122,7 +123,7 @@ public class UniversalBucket extends Item
     }
 
     @Override
-    public String getItemStackDisplayName(ItemStack stack)
+    public String getItemStackDisplayName(@Nonnull ItemStack stack)
     {
         FluidStack fluidStack = getFluid(stack);
         if (fluidStack == null)
@@ -272,7 +273,7 @@ public class UniversalBucket extends Item
         return bucket;
     }
 
-    public FluidStack getFluid(ItemStack container)
+    public FluidStack getFluid(@Nonnull ItemStack container)
     {
         return FluidStack.loadFluidStackFromNBT(container.getTagCompound());
     }

src/main/java/net/minecraftforge/fml/common/gameevent/PlayerEvent.java

@@ -25,6 +25,8 @@ import net.minecraft.inventory.IInventory;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.fml.common.eventhandler.Event;
 
+import javax.annotation.Nonnull;
+
 public class PlayerEvent extends Event {
     public final EntityPlayer player;
     private PlayerEvent(EntityPlayer player)
@@ -42,9 +44,10 @@ public class PlayerEvent extends Event {
     }
 
     public static class ItemCraftedEvent extends PlayerEvent {
+        @Nonnull
         public final ItemStack crafting;
         public final IInventory craftMatrix;
-        public ItemCraftedEvent(EntityPlayer player, ItemStack crafting, IInventory craftMatrix)
+        public ItemCraftedEvent(EntityPlayer player, @Nonnull ItemStack crafting, IInventory craftMatrix)
         {
             super(player);
             this.crafting = crafting;
@@ -52,8 +55,9 @@ public class PlayerEvent extends Event {
         }
     }
     public static class ItemSmeltedEvent extends PlayerEvent {
+        @Nonnull
         public final ItemStack smelting;
-        public ItemSmeltedEvent(EntityPlayer player, ItemStack crafting)
+        public ItemSmeltedEvent(EntityPlayer player, @Nonnull ItemStack crafting)
         {
             super(player);
             this.smelting = crafting;

src/main/java/net/minecraftforge/fml/common/registry/GameRegistry.java

@@ -67,6 +67,8 @@ import com.google.common.collect.ObjectArrays;
 import com.google.common.collect.Sets;
 import com.google.common.primitives.Ints;
 
+import javax.annotation.Nonnull;
+
 @SuppressWarnings({"WeakerAccess", "unused"})
 public class GameRegistry
 {
@@ -220,17 +222,17 @@ public class GameRegistry
         GameData.getMain().registerSubstitutionAlias(nameToSubstitute, type, object);
     }
 
-    public static void addRecipe(ItemStack output, Object... params)
+    public static void addRecipe(@Nonnull ItemStack output, Object... params)
     {
         addShapedRecipe(output, params);
     }
 
-    public static IRecipe addShapedRecipe(ItemStack output, Object... params)
+    public static IRecipe addShapedRecipe(@Nonnull ItemStack output, Object... params)
     {
         return CraftingManager.getInstance().addRecipe(output, params);
     }
 
-    public static void addShapelessRecipe(ItemStack output, Object... params)
+    public static void addShapelessRecipe(@Nonnull ItemStack output, Object... params)
     {
         CraftingManager.getInstance().addShapelessRecipe(output, params);
     }
@@ -240,17 +242,17 @@ public class GameRegistry
         CraftingManager.getInstance().getRecipeList().add(recipe);
     }
 
-    public static void addSmelting(Block input, ItemStack output, float xp)
+    public static void addSmelting(Block input, @Nonnull ItemStack output, float xp)
     {
         FurnaceRecipes.instance().addSmeltingRecipeForBlock(input, output, xp);
     }
 
-    public static void addSmelting(Item input, ItemStack output, float xp)
+    public static void addSmelting(Item input, @Nonnull ItemStack output, float xp)
     {
         FurnaceRecipes.instance().addSmelting(input, output, xp);
     }
 
-    public static void addSmelting(ItemStack input, ItemStack output, float xp)
+    public static void addSmelting(@Nonnull ItemStack input, @Nonnull ItemStack output, float xp)
     {
         FurnaceRecipes.instance().addSmeltingRecipe(input, output, xp);
     }
@@ -282,7 +284,7 @@ public class GameRegistry
         fuelHandlers.add(handler);
     }
 
-    public static int getFuelValue(ItemStack itemStack)
+    public static int getFuelValue(@Nonnull ItemStack itemStack)
     {
         int fuelValue = 0;
         for (IFuelHandler handler : fuelHandlers)
@@ -362,6 +364,7 @@ public class GameRegistry
      * @param nbtString an nbt stack as a string, will be processed by {@link JsonToNBT}
      * @return a new itemstack
      */
+    @Nonnull
     public static ItemStack makeItemStack(String itemName, int meta, int stackSize, String nbtString)
     {
         if (itemName == null)
@@ -372,7 +375,7 @@ public class GameRegistry
         if (item == null)
         {
             FMLLog.getLogger().log(Level.TRACE, "Unable to find item with name {}", itemName);
-            return null;
+            return ItemStack.field_190927_a;
         }
         ItemStack is = new ItemStack(item, stackSize, meta);
         if (!Strings.isNullOrEmpty(nbtString))

src/main/java/net/minecraftforge/items/ItemHandlerHelper.java

@@ -50,9 +50,9 @@ public class ItemHandlerHelper
         return stack;
     }
 
-    public static boolean canItemStacksStack(ItemStack a, ItemStack b)
+    public static boolean canItemStacksStack(@Nonnull ItemStack a, @Nonnull ItemStack b)
     {
-        if (a == null || !a.isItemEqual(b))
+        if (a.func_190926_b() || !a.isItemEqual(b))
             return false;
 
         final NBTTagCompound aTag = a.getTagCompound();
@@ -64,9 +64,9 @@ public class ItemHandlerHelper
      * A relaxed version of canItemStacksStack that stacks itemstacks with different metadata if they don't have subtypes.
      * This usually only applies when players pick up items.
      */
-    public static boolean canItemStacksStackRelaxed(ItemStack a, ItemStack b)
+    public static boolean canItemStacksStackRelaxed(@Nonnull ItemStack a, @Nonnull ItemStack b)
     {
-        if (a == null || b == null || a.getItem() != b.getItem())
+        if (a.func_190926_b() || b.func_190926_b() || a.getItem() != b.getItem())
             return false;
 
         if (!a.isStackable())
@@ -84,7 +84,7 @@ public class ItemHandlerHelper
     }
 
     @Nonnull
-    public static ItemStack copyStackWithSize(ItemStack itemStack, int size)
+    public static ItemStack copyStackWithSize(@Nonnull ItemStack itemStack, int size)
     {
         if (size == 0)
             return ItemStack.field_190927_a;
@@ -148,7 +148,7 @@ public class ItemHandlerHelper
     }
 
     /** giveItemToPlayer without preferred slot */
-    public static void giveItemToPlayer(EntityPlayer player, ItemStack stack) {
+    public static void giveItemToPlayer(EntityPlayer player, @Nonnull ItemStack stack) {
         giveItemToPlayer(player, stack, -1);
     }
 
@@ -159,7 +159,7 @@ public class ItemHandlerHelper
      * @param player The player to give the item to
      * @param stack  The itemstack to insert
      */
-    public static void giveItemToPlayer(EntityPlayer player, ItemStack stack, int preferredSlot)
+    public static void giveItemToPlayer(EntityPlayer player, @Nonnull ItemStack stack, int preferredSlot)
     {
         IItemHandler inventory = new PlayerMainInvWrapper(player.inventory);
         World world = player.worldObj;
@@ -172,20 +172,20 @@ public class ItemHandlerHelper
             remainder = inventory.insertItem(preferredSlot, stack, false);
         }
         // then into the inventory in general
-        if(remainder != null)
+        if(!remainder.func_190926_b())
         {
             remainder = insertItemStacked(inventory, remainder, false);
         }
 
         // play sound if something got picked up
-        if (remainder == null || remainder.func_190916_E() != stack.func_190916_E())
+        if (remainder.func_190926_b() || remainder.func_190916_E() != stack.func_190916_E())
         {
             world.playSound(player, player.posX, player.posY, player.posZ,
                     SoundEvents.ENTITY_ITEM_PICKUP, SoundCategory.PLAYERS, 0.2F, ((world.rand.nextFloat() - world.rand.nextFloat()) * 0.7F + 1.0F) * 2.0F);
         }
 
         // drop remaining itemstack into the world
-        if (remainder != null && !world.isRemote)
+        if (!remainder.func_190926_b() && !world.isRemote)
         {
             EntityItem entityitem = new EntityItem(world, player.posX, player.posY + 0.5, player.posZ, stack);
             entityitem.setPickupDelay(40);

src/main/java/net/minecraftforge/items/ItemStackHandler.java

@@ -154,7 +154,7 @@ public class ItemStackHandler implements IItemHandler, IItemHandlerModifiable, I
         }
     }
 
-    protected int getStackLimit(int slot, ItemStack stack)
+    protected int getStackLimit(int slot, @Nonnull ItemStack stack)
     {
         return stack.getMaxStackSize();
     }

src/main/java/net/minecraftforge/items/VanillaHopperItemHandler.java

@@ -39,7 +39,7 @@ public class VanillaHopperItemHandler extends InvWrapper
     @Nonnull
     public ItemStack insertItem(int slot, @Nonnull ItemStack stack, boolean simulate)
     {
-        if (stack == null)
+        if (stack.func_190926_b())
             return null;
 //        if (simulate || !hopper.mayTransfer())
 //            return super.insertItem(slot, stack, simulate);

src/main/java/net/minecraftforge/items/VanillaInventoryCodeHooks.java

@@ -47,15 +47,15 @@ public class VanillaInventoryCodeHooks
         for (int i = 0; i < handler.getSlots(); i++)
         {
             ItemStack extractItem = handler.extractItem(i, 1, true);
-            if (extractItem != null)
+            if (!extractItem.func_190926_b())
             {
                 for (int j = 0; j < dest.getSizeInventory(); j++)
                 {
                     ItemStack destStack = dest.getStackInSlot(j);
-                    if (destStack == null || destStack.func_190916_E() < destStack.getMaxStackSize() && destStack.func_190916_E() < dest.getInventoryStackLimit() && ItemHandlerHelper.canItemStacksStack(extractItem, destStack))
+                    if (destStack.func_190926_b() || destStack.func_190916_E() < destStack.getMaxStackSize() && destStack.func_190916_E() < dest.getInventoryStackLimit() && ItemHandlerHelper.canItemStacksStack(extractItem, destStack))
                     {
                         extractItem = handler.extractItem(i, 1, false);
-                        if (destStack == null)
+                        if (destStack.func_190926_b())
                             dest.setInventorySlotContents(j, extractItem);
                         else
                         {
@@ -120,7 +120,7 @@ public class VanillaInventoryCodeHooks
         for (int i = 0; i < hopper.getSizeInventory(); i++)
         {
             ItemStack stackInSlot = hopper.getStackInSlot(i);
-            if (stackInSlot != null)
+            if (stackInSlot.func_190926_b())
             {
                 ItemStack insert = stackInSlot.copy();
                 insert.func_190920_e(1);

src/main/java/net/minecraftforge/items/wrapper/InvWrapper.java

@@ -72,8 +72,8 @@ public class InvWrapper implements IItemHandlerModifiable
     @Nonnull
     public ItemStack insertItem(int slot, @Nonnull ItemStack stack, boolean simulate)
     {
-        if (stack == null)
+        if (stack.func_190926_b())
-            return null;
+            return ItemStack.field_190927_a;
 
         if (!getInv().isItemValidForSlot(slot, stack))
             return stack;
@@ -98,7 +98,7 @@ public class InvWrapper implements IItemHandlerModifiable
                     getInv().markDirty();
                 }
 
-                return null;
+                return ItemStack.field_190927_a;
             }
             else
             {
@@ -145,7 +145,7 @@ public class InvWrapper implements IItemHandlerModifiable
                     getInv().setInventorySlotContents(slot, stack);
                     getInv().markDirty();
                 }
-                return null;
+                return ItemStack.field_190927_a;
             }
         }
 
@@ -156,12 +156,12 @@ public class InvWrapper implements IItemHandlerModifiable
     public ItemStack extractItem(int slot, int amount, boolean simulate)
     {
         if (amount == 0)
-            return null;
+            return ItemStack.field_190927_a;
 
         ItemStack stackInSlot = getInv().getStackInSlot(slot);
 
-        if (stackInSlot == null)
+        if (stackInSlot.func_190926_b())
-            return null;
+            return ItemStack.field_190927_a;
 
         if (simulate)
         {
@@ -187,7 +187,7 @@ public class InvWrapper implements IItemHandlerModifiable
     }
 
     @Override
-    public void setStackInSlot(int slot, ItemStack stack)
+    public void setStackInSlot(int slot, @Nonnull ItemStack stack)
     {
         getInv().setInventorySlotContents(slot, stack);
     }

src/main/java/net/minecraftforge/items/wrapper/RangedWrapper.java

@@ -58,7 +58,7 @@ public class RangedWrapper implements IItemHandlerModifiable {
             return compose.getStackInSlot(slot + minSlot);
         }
 
-        return null;
+        return ItemStack.field_190927_a;
     }
 
     @Override
@@ -86,7 +86,7 @@ public class RangedWrapper implements IItemHandlerModifiable {
     }
 
     @Override
-    public void setStackInSlot(int slot, ItemStack stack)
+    public void setStackInSlot(int slot, @Nonnull ItemStack stack)
     {
         if (checkSlot(slot))
         {

src/main/java/net/minecraftforge/oredict/OreDictionary.java

@@ -653,6 +653,7 @@ public class OreDictionary
             return Name;
         }
 
+        @Nonnull
         public ItemStack getOre()
         {
             return Ore;