flutter unhandled exception

import 'dart:async';
import 'package:flutter/material.dart';

void main() =>
  runZoned<Future<void>>(
    () async {
      runApp(MyApp());
    },
    onError: (dynamic error, StackTrace stackTrace) {
      print("=================== CAUGHT DART ERROR");
      // Send report
      // NEVER REACHES HERE - WHY?
    },
  );

class MyApp extends StatefulWidget {
  // This widget is the root of your application.
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  @override
  void initState() {
    super.initState();

    // This captures errors reported by the FLUTTER framework.
    FlutterError.onError = (FlutterErrorDetails details) {
      print("=================== CAUGHT FLUTTER ERROR");
      // Send report
      // NEVER REACHES HERE - WHY?
    };
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: RaisedButton(
            child: Text("Throw exception"),
            onPressed: () {
              throw Exception("This is a test exception");
            },
          ),
        ),
      ),
    );
  }
}