Flutter ScreenState Dispose方法异常

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

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  StreamSubscription<String> _subscription;
  Stream<String> _stream;

  @override
  void initState() {
    super.initState();
    _stream = getStream(); // 假设这是一个获取 Stream 的方法
    _subscription = _stream.listen((data) {
      print(data);
    });
  }

  @override
  void dispose() {
    _subscription.cancel(); // 取消订阅
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container(); // 返回一个简单的容器
  }

  Stream<String> getStream() async* {
    yield 'Hello';
    yield 'World';
  }
}