SPIGOT-4842: Dummy recipes should not give AIR as result type

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

paper-api/src/main/java/org/bukkit/inventory/CookingRecipe.java

@@ -42,6 +42,7 @@ public abstract class CookingRecipe<T extends CookingRecipe> implements Recipe,
      * @param cookingTime The cooking time (in ticks)
      */
     public CookingRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result, @NotNull RecipeChoice input, float experience, int cookingTime) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = key;
         this.output = new ItemStack(result);
         this.ingredient = input;

paper-api/src/main/java/org/bukkit/inventory/ShapedRecipe.java

@@ -23,6 +23,7 @@ public class ShapedRecipe implements Recipe, Keyed {
 
     @Deprecated
     public ShapedRecipe(@NotNull ItemStack result) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = NamespacedKey.randomKey();
         this.output = new ItemStack(result);
     }
@@ -41,6 +42,7 @@ public class ShapedRecipe implements Recipe, Keyed {
      */
     public ShapedRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result) {
         Preconditions.checkArgument(key != null, "key");
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
 
         this.key = key;
         this.output = new ItemStack(result);

paper-api/src/main/java/org/bukkit/inventory/ShapelessRecipe.java

@@ -24,6 +24,7 @@ public class ShapelessRecipe implements Recipe, Keyed {
 
     @Deprecated
     public ShapelessRecipe(@NotNull ItemStack result) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = NamespacedKey.randomKey();
         this.output = new ItemStack(result);
     }
@@ -43,6 +44,7 @@ public class ShapelessRecipe implements Recipe, Keyed {
      * @see ShapelessRecipe#addIngredient(int,Material,int)
      */
     public ShapelessRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = key;
         this.output = new ItemStack(result);
     }

paper-api/src/main/java/org/bukkit/inventory/StonecuttingRecipe.java

@@ -35,6 +35,7 @@ public class StonecuttingRecipe implements Recipe, Keyed {
      * @param input The input choices.
      */
     public StonecuttingRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result, @NotNull RecipeChoice input) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = key;
         this.output = new ItemStack(result);
         this.ingredient = input;