Cannot read property 'Symbol(dartx._get)' of null

Question

I'm trying to call API in the web app is show this error and Android and iOS Working fine. I don't understand why happening.I'm using retrofit and dio to call api's.

   import 'dart:convert';
    import 'package:flutter/cupertino.dart';
    import 'package:web_app/utils/constants.dart';
    
    class ServiceError {
      static BuildContext context;
    
      ServiceError(BuildContext context) {
        context = context;
      }
    
      void getError(final res) {
print("MyError" + res.toString()); // I got null value and this working fine in android and iOS. only i get problem in web app
        final jsonResponse = jsonDecode(res.toString());
        ApiError apiError = ApiError.fromJson(jsonResponse);
        print("MyError" + apiError.status);
        print("MyCode" + apiError.message);
    
        if (apiError.responseCode == 500) {
          Constants.toast(apiError.message);
        } else {
          Constants.toast(apiError.message);
        }
      }
    }

I got this error

TypeError: Cannot read property 'Symbol(dartx._get)' of null
    at new service_errors.ApiError.fromJson (http://localhost:44059/packages/web_app/service_errors/service_errors.dart.lib.js:103:36)
    at service_errors.ServiceError.new.getError (http://localhost:44059/packages/web_app/service_errors/service_errors.dart.lib.js:23:22)
    at http://localhost:44059/packages/web_app/forgot_password/reset_password.dart.lib.js:6485:58
    at _RootZone.runUnary (http://localhost:44059/dart_sdk.js:37533:58)
    at _FutureListener.catchError.handleError (http://localhost:44059/dart_sdk.js:32521:48)
    at handleError (http://localhost:44059/dart_sdk.js:33070:51)
    at Function._propagateToListeners (http://localhost:44059/dart_sdk.js:33096:17)
    at _Future.new.[_completeError] (http://localhost:44059/dart_sdk.js:32943:23)
    at async._AsyncCallbackEntry.new.callback (http://localhost:44059/dart_sdk.js:32981:31)
    at Object._microtaskLoop (http://localhost:44059/dart_sdk.js:37794:13)
    at _startMicrotaskLoop (http://localhost:44059/dart_sdk.js:37800:13)
    at http://localhost:44059/dart_sdk.js:33309:9

Not realy sure what is actually causing the issue, hope you can help. Thank you so mush.

Solution 1

CORS Related Issue

My Flutter Web app communicates with an Azure Function. The iOS and Android versions worked fine, but I was getting the property 'Symbol(dartx._get)' of null error above when attempting to execute a graphql query against the azure function in flutter web. Chetan's CORS hint in the comment above gave me a clue.

This Stack Overflow Q&A resolved the issues I have having on production and localhost. CORS with Azure function from localhost (not CLI)

• Localhost Solution
• Production Solution

Solution 2

Sometimes it may happen due to uninitialized Map Fields on set operation, So initialze it,

Map<String> jsonResult;

To

Map<String> jsonResult={};