The argument type 'ProductModel?' can't be assigned to the parameter type 'ProductModel' - flutter

Question

I'm making a midel to upload product image,price and name to firebase then i face this error (The argument type 'ProductModel?' can't be assigned to the parameter type 'ProductModel'.)
class ProductProvider with ChangeNotifier {
List<ProductModel> pizzaProductList = [];
ProductModel? productModel;
fatchPizzaproductData() async {
// List<ProductModel> newList = [];
QuerySnapshot value =
await FirebaseFirestore.instance.collection("PizzaProducts").get();
pizzaProductList = value.docs.map((element) {
return ProductModel(
productImage: element.get("productImage"),
productName: element.get("productName"),
productPrice: element.get("productPrice"),
);
}).toList();
}
get getPizzaproductDataList {
return pizzaProductList;
}
}

Answer 1

The problem is that productModel is a nullable type, whereas pizzaProduct is a List of non-nullable ProductModels.
Instead of storing a property productModel on your class, consider mapping directly from value.docs to pizzaProduct, and removing the intermediate step of storing the model in productModel:
class ProductProvider with ChangeNotifier {
List<ProductModel> pizzaProduct = [];
Future<void> fetchPizzaProductData() async {
QuerySnapshot value =
await FirebaseFirestore.instance.collection("PizzaProducts").get();
pizzaProduct = value.docs.map((element) {
return ProductModel(
productImage: element.get("productImage"),
productName: element.get("productName"),
productPrice: element.get("productPrice"),
);
}).toList();
// Since this is a ChangeNotifier, I'm assuming you might want to
// notify listeners when `pizzaProduct` changes. Disregard this line
// if that's not the case.
notifyListeners();
}
}