changed recipe class

lib/services/providers/recipe_provider.dart

@@ -23,6 +23,13 @@ class RecipeProvider extends ChangeNotifier {
     }
   }
 
+  void updateServingSize(int servingSize, {bool silent = false}) {
+    _recipe = _recipe.copyWith(servingSize: servingSize);
+    if (!silent) {
+      notifyListeners();
+    }
+  }
+
   void updateDifficulty(Difficulty difficulty, {bool silent = false}) {
     _recipe = _recipe.copyWith(difficulty: difficulty);
     if (!silent) {
@@ -73,14 +80,14 @@ class RecipeProvider extends ChangeNotifier {
     }
   }
 
-  void updateMealCategory(MealCategory mealCategory, {bool silent = false}) {
+  void updateMealCategory(MealCategory? mealCategory, {bool silent = false}) {
     _recipe = _recipe.copyWith(mealCategory: mealCategory);
     if (!silent) {
       notifyListeners();
     }
   }
 
-  void updateCuisine(Cuisine cuisine, {bool silent = false}) {
+  void updateCuisine(Cuisine? cuisine, {bool silent = false}) {
     _recipe = _recipe.copyWith(cuisine: cuisine);
     if (!silent) {
       notifyListeners();