Firebase realtime database onValue event don't work

[guvenacar]

I have firebase realtime database. When I manually change data on the Firebase console, vscode stops responding and throws the following error. What is wrong in my code?

Error: TypeError: Instance of '_Exception': type '_Exception' is not a subtype of type 'JavaScriptObject'

main.dart

import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/material.dart';
import 'package:realtimedbtest/firebase_options.dart';

String result = "";

void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp(
options: DefaultFirebaseOptions.currentPlatform,
);

DatabaseReference ref = FirebaseDatabase.instance.ref('widget/image/name');
ref.onValue.listen((DatabaseEvent event) {
result = event.snapshot.value.toString();
});

runApp(const MainApp());
}

class MainApp extends StatelessWidget {
const MainApp({super.key});

@OverRide
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: Text("result: $result"),
),
),
);
}
}