no firebase app has been created in flutter code example

Example 1: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp() flutter

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

Example 2: no firebase app ' default ' has been created flutter

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}