Replace Non created materials/parts with null item definitions instead of null.

core/features/NullItemDefinition.java

@@ -0,0 +1,42 @@
+package appeng.core.features;
+
+import net.minecraft.block.Block;
+import net.minecraft.item.Item;
+import net.minecraft.item.ItemStack;
+import net.minecraft.tileentity.TileEntity;
+import appeng.api.util.AEItemDefinition;
+
+public class NullItemDefinition implements AEItemDefinition
+{
+
+	@Override
+	public Block block()
+	{
+		return null;
+	}
+
+	@Override
+	public Item item()
+	{
+		return null;
+	}
+
+	@Override
+	public Class<? extends TileEntity> entity()
+	{
+		return null;
+	}
+
+	@Override
+	public ItemStack stack(int stackSize)
+	{
+		return null;
+	}
+
+	@Override
+	public boolean sameAs(ItemStack comparableItem)
+	{
+		return false;
+	}
+
+}