Remove unit test based on now incorrect assumptions

By: md_5 <git@md-5.net>

paper-server/src/test/java/org/bukkit/craftbukkit/inventory/NMSCraftItemStackTest.java

@@ -25,12 +25,4 @@ public class NMSCraftItemStackTest extends AbstractTestingBase {
         assertThat(clone.getData(), is(itemStack.getData()));
         assertThat(clone, is(itemStack));
     }
-
-    @Test
-    public void testCloneNullItem() throws Exception {
-        net.minecraft.server.ItemStack nmsItemStack = null;
-        ItemStack itemStack = CraftItemStack.asCraftMirror(nmsItemStack);
-        ItemStack clone = itemStack.clone();
-        assertThat(clone, is(itemStack));
-    }
 }