fix creating complex recipes that have air results

Fixes #10715

patches/api/0479-Improve-Recipe-validation.patch

@@ -170,14 +170,14 @@ index beb798482479c58a8628c314b510ab6349576ce8..6a8195ca224790e3130ec9923188e7b5
              ingredients.add(new RecipeChoice.ExactChoice(item));
          }
 diff --git a/src/main/java/org/bukkit/inventory/SmithingRecipe.java b/src/main/java/org/bukkit/inventory/SmithingRecipe.java
-index 1ef9a715a2736e88a16083c6873803a8bd6bcf29..99e40588c10141391762f37b5a326f8df06e5276 100644
+index 1ef9a715a2736e88a16083c6873803a8bd6bcf29..a8f451dc1d8d49c2080c3ed3d8348020c3d470cf 100644
 --- a/src/main/java/org/bukkit/inventory/SmithingRecipe.java
 +++ b/src/main/java/org/bukkit/inventory/SmithingRecipe.java
 @@ -44,12 +44,13 @@ public class SmithingRecipe implements Recipe, Keyed {
       */
      @Deprecated
      public SmithingRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result, @NotNull RecipeChoice base, @NotNull RecipeChoice addition, boolean copyDataComponents) {
-+        com.google.common.base.Preconditions.checkArgument(!result.isEmpty(), "Recipe cannot have an empty result."); // Paper
++        com.google.common.base.Preconditions.checkArgument(!result.isEmpty() || this instanceof ComplexRecipe, "Recipe cannot have an empty result."); // Paper
          this.copyDataComponents = copyDataComponents;
          // Paper end
          this.key = key;