First batch of null -> isEmpty() checks.

I most likely still missed a ton of checks...

src/main/java/appeng/core/features/ColoredItemDefinition.java

@@ -92,7 +92,7 @@ public final class ColoredItemDefinition implements AEColoredItemDefinition
 	{
 		final ItemStackSrc is = this.colors[color.ordinal()];
 
-		if( comparableItem == null || is == null )
+		if( comparableItem.isEmpty() || is == null )
 		{
 			return false;
 		}

src/main/java/appeng/core/features/registries/cell/CellRegistry.java

@@ -53,7 +53,7 @@ public class CellRegistry implements ICellRegistry
 	@Override
 	public boolean isCellHandled( final ItemStack is )
 	{
-		if( is == null )
+		if( is.isEmpty() )
 		{
 			return false;
 		}
@@ -70,7 +70,7 @@ public class CellRegistry implements ICellRegistry
 	@Override
 	public ICellHandler getHandler( final ItemStack is )
 	{
-		if( is == null )
+		if( is.isEmpty() )
 		{
 			return null;
 		}
@@ -87,7 +87,7 @@ public class CellRegistry implements ICellRegistry
 	@Override
 	public IMEInventoryHandler getCellInventory( final ItemStack is, final ISaveProvider container, final StorageChannel chan )
 	{
-		if( is == null )
+		if( is.isEmpty() )
 		{
 			return null;
 		}

src/main/java/appeng/core/features/registries/cell/CreativeCellHandler.java

@@ -42,13 +42,13 @@ public class CreativeCellHandler implements ICellHandler
 	@Override
 	public boolean isCell( final ItemStack is )
 	{
-		return is != null && is.getItem() instanceof ItemCreativeStorageCell;
+		return !is.isEmpty() && is.getItem() instanceof ItemCreativeStorageCell;
 	}
 
 	@Override
 	public IMEInventoryHandler getCellInventory( final ItemStack is, final ISaveProvider container, final StorageChannel channel )
 	{
-		if( channel == StorageChannel.ITEMS && is != null && is.getItem() instanceof ItemCreativeStorageCell )
+		if( channel == StorageChannel.ITEMS && !is.isEmpty() && is.getItem() instanceof ItemCreativeStorageCell )
 		{
 			return CreativeCellInventory.getCell( is );
 		}

src/main/java/appeng/core/features/registries/grinder/GrinderRecipeManager.java

@@ -229,7 +229,7 @@ public final class GrinderRecipeManager implements IGrinderRegistry, IOreListene
 
 	private ItemStack copy( final ItemStack is )
 	{
-		if( is != null )
+		if( !is.isEmpty() )
 		{
 			return is.copy();
 		}

src/main/java/appeng/core/features/registries/inscriber/InscriberRegistry.java

@@ -182,11 +182,11 @@ public final class InscriberRegistry implements IInscriberRegistry
 			{
 				throw new IllegalStateException( "Input must have a size." );
 			}
-			if( this.output == null )
+			if( this.output.isEmpty() )
 			{
 				throw new IllegalStateException( "Output must be defined." );
 			}
-			if( this.topOptional == null && this.bottomOptional == null )
+			if( this.topOptional.isEmpty() && this.bottomOptional.isEmpty() )
 			{
 				throw new IllegalStateException( "One optional must be defined." );
 			}