Use ItemStack.empty() when air is passed into constructor

patches/api/Proxy-ItemStack-to-CraftItemStack.patch

@@ -89,7 +89,9 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
          }
 -        this.type = type;
 -        this.amount = amount;
-+        this.craftDelegate = ItemStack.of(type, amount); // Paper - create delegate
++        // Paper start - create delegate
++        this.craftDelegate = type == Material.AIR ? ItemStack.empty() : ItemStack.of(type, amount);
++        // Paper end - create delegate
          if (damage != 0) {
              setDurability(damage);
          }