First batch of null -> isEmpty() checks.

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

src/main/java/appeng/client/me/ItemRepo.java

@@ -84,7 +84,7 @@ public class ItemRepo
 
 		if( idx >= this.dsp.size() )
 		{
-			return null;
+			return ItemStack.EMPTY;
 		}
 		return this.dsp.get( idx );
 	}

src/main/java/appeng/client/me/SlotDisconnected.java

@@ -63,11 +63,11 @@ public class SlotDisconnected extends AppEngSlot
 		if( Platform.isClient() )
 		{
 			final ItemStack is = super.getStack();
-			if( is != null && is.getItem() instanceof ItemEncodedPattern )
+			if( !is.isEmpty() && is.getItem() instanceof ItemEncodedPattern )
 			{
 				final ItemEncodedPattern iep = (ItemEncodedPattern) is.getItem();
 				final ItemStack out = iep.getOutput( is );
-				if( out != null )
+				if( !out.isEmpty() )
 				{
 					return out;
 				}

src/main/java/appeng/client/me/SlotME.java

@@ -60,7 +60,7 @@ public class SlotME extends Slot
 		{
 			return this.mySlot.getStack();
 		}
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override
@@ -68,7 +68,7 @@ public class SlotME extends Slot
 	{
 		if( this.mySlot.hasPower() )
 		{
-			return this.getStack() != null;
+			return !this.getStack().isEmpty();
 		}
 		return false;
 	}
@@ -88,7 +88,7 @@ public class SlotME extends Slot
 	@Override
 	public ItemStack decrStackSize( final int par1 )
 	{
-		return null;
+		return ItemStack.EMPTY;
 	}
 
 	@Override