Changed to Null ItemStack instead of null.

src/main/java/appeng/container/AEBaseContainer.java

@@ -455,7 +455,7 @@ public abstract class AEBaseContainer extends Container
 	{
 		if( Platform.isClient() )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 
 		boolean hasMETiles = false;
@@ -470,14 +470,14 @@ public abstract class AEBaseContainer extends Container
 
 		if( hasMETiles && Platform.isClient() )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 
 		final AppEngSlot clickSlot = (AppEngSlot) this.inventorySlots.get( idx ); // require AE SLots!
 
 		if( clickSlot instanceof SlotDisabled || clickSlot instanceof SlotInaccessible )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 		if( clickSlot != null && clickSlot.getHasStack() )
 		{
@@ -485,7 +485,7 @@ public abstract class AEBaseContainer extends Container
 
 			if( tis == null )
 			{
-				return null;
+				return ItemStack.EMPTY;
 			}
 
 			final List<Slot> selectedSlots = new ArrayList<Slot>();
@@ -602,7 +602,7 @@ public abstract class AEBaseContainer extends Container
 
 									this.updateSlot( clickSlot );
 									this.updateSlot( d );
-									return null;
+									return ItemStack.EMPTY;
 								}
 								else
 								{
@@ -656,7 +656,7 @@ public abstract class AEBaseContainer extends Container
 
 									this.updateSlot( clickSlot );
 									this.updateSlot( d );
-									return null;
+									return ItemStack.EMPTY;
 								}
 								else
 								{
@@ -692,7 +692,7 @@ public abstract class AEBaseContainer extends Container
 
 								this.updateSlot( clickSlot );
 								this.updateSlot( d );
-								return null;
+								return ItemStack.EMPTY;
 							}
 							else
 							{
@@ -707,7 +707,7 @@ public abstract class AEBaseContainer extends Container
 		}
 
 		this.updateSlot( clickSlot );
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override

src/main/java/appeng/container/implementations/ContainerQuartzKnife.java

@@ -128,9 +128,9 @@ public class ContainerQuartzKnife extends AEBaseContainer implements IAEAppEngIn
 	public ItemStack getStackInSlot( final int var1 )
 	{
 		final ItemStack input = this.inSlot.getStackInSlot( 0 );
-		if( input == null )
+		if( input == ItemStack.EMPTY )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 
 		if( SlotRestrictedInput.isMetalIngot( input ) )
@@ -147,7 +147,7 @@ public class ContainerQuartzKnife extends AEBaseContainer implements IAEAppEngIn
 			}
 		}
 
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override
@@ -161,7 +161,7 @@ public class ContainerQuartzKnife extends AEBaseContainer implements IAEAppEngIn
 				return is;
 			}
 		}
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	private boolean makePlate()
@@ -185,7 +185,7 @@ public class ContainerQuartzKnife extends AEBaseContainer implements IAEAppEngIn
 	@Override
 	public ItemStack removeStackFromSlot( final int var1 )
 	{
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override

src/main/java/appeng/container/slot/AppEngSlot.java

@@ -85,12 +85,12 @@ public class AppEngSlot extends Slot
 	{
 		if( !this.isEnabled() )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 
 		if( this.inventory.getSizeInventory() <= this.getSlotIndex() )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 
 		if( this.isDisplay() )

src/main/java/appeng/container/slot/NullSlot.java

@@ -54,7 +54,7 @@ public class NullSlot extends Slot
 	@Override
 	public ItemStack getStack()
 	{
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override
@@ -78,7 +78,7 @@ public class NullSlot extends Slot
 	@Override
 	public ItemStack decrStackSize( final int par1 )
 	{
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override

src/main/java/appeng/container/slot/SlotCraftingTerm.java

@@ -200,7 +200,7 @@ public class SlotCraftingTerm extends AppEngCraftingSlot
 							return request;
 						}
 					}
-					return null;
+					return ItemStack.EMPTY;
 				}
 
 				is = r.getCraftingResult( ic );
@@ -231,7 +231,7 @@ public class SlotCraftingTerm extends AppEngCraftingSlot
 			return is;
 		}
 
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	private boolean preCraft( final EntityPlayer p, final IMEMonitor<IAEItemStack> inv, final ItemStack[] set, final ItemStack result )

src/main/java/appeng/container/slot/SlotFake.java

@@ -41,7 +41,7 @@ public class SlotFake extends AppEngSlot
 	@Override
 	public ItemStack decrStackSize( final int par1 )
 	{
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override