return Future.value is null in Freezed .when method

I am using Freezed package to create NetworkResponse class to use with Networking manager. I return Future.value(cartFetched) in getCartData method and access it in fetchCart but value in Future.then method is always null. If I change the getCartData method to return Future<ActionEnum> then compiler makes me return a Action value at the end which overwrites/supersedes my return Future.value(ActionEnum.cartFetched) inside cartData.when method. How can I return a valid value from getCartData?

        class CartRepository {

            Future<void> getCartData(Map<String, Object> requestData) async {
            CartEndPoint cart = CartEndPoint();
            cart.requestBody = requestData;
            try {
              NetworkResponse? cartData = await apiManager.fetchData(loginEnd);
        
              cartData.when(success: (response) {
                return Future.value(ActionEnum.cartFetched); // Action is a enum
              }, loading: (message) {
                print("loading -  ${message}");
              }, error: (error) {
                print("error -  ${error.message}");
                throw error;
              });
            } catch (error) {
              rethrow;
                }
              }
        }

        class _CartScreenState extends State<CartScreen> {

            fetchCart() {
            Future service = CartRepository(). getCartData(requestData);
            service.then((value) {
            **// value is always null**
              if (value is ActionEnum) {
                switch (value) {
                  case ActionEnum.cartFetched:
                    // do next action
                    break;
                }
              }
              
              widget.onChange(true);
            }).onError((error, stackTrace) {
              print(error);
            });
    }
    }

First, you need to change the return type of getCartData from Future to Future or, in case you want to make it nullable, Future<ActionEnum?>. Then, inside getCartData(), you need to add return before cartData(success: (response)), because the return inside cartData(success: (response)) only returns to that function call, not to getCartData.

Code:

    class CartRepository {
  Future<ActionEnum> getCartData(Map<String, Object> requestData) async {
    CartEndPoint cart = CartEndPoint();
    cart.requestBody = requestData;
    try {
      NetworkResponse? cartData = await apiManager.fetchData(loginEnd);

     return cartData(success: (response) {
        return Future.value(ActionEnum.cartFetched); // Action is a enum
      }, loading: (message) {
        print("loading -  ${message}");
        //Here you need to throw or return something or incase you use nullable then return null
      }, error: (error) {
        print("error -  ${error.message}");
        throw error;
      });
    } catch (error) {
      rethrow;
    }
  }
}

I hope it helps.