我正在尝试学习Flutter，这是一个从培训复制代码，我不知道该怎么做来修复它。
错误：
对设备sdk gphone64 x86 64使用硬件呈现。如果注意到图形失真，请考虑使用"--enable-software-rendering"启用软件呈现。在调试模式下在sdk gphone64 x86 64上启动lib\main. dart ... lib/main. dart：31：19：错误：参数"key"不能具有值"null"，因为其类型为"Key"，但隐式默认值为"null"。

• "键"来自"package：flutter/src/foundation/key. dart"（'/C：/flutter/flutter/packages/flutter/lib/src/foundation/key. dart'）。请尝试添加显式的非"null"默认值或"required"修饰符。MyHomePage（{Key key，this. title}）：超级（键：键）;^^^lib/主文件夹。日期：31：29：错误：参数"title"的值不能为"null"，因为其类型为"String"，但隐式默认值为"null"。请尝试添加显式非"null"默认值或"required"修饰符。MyHomePage（{Key key，this. title}）：超级（键：键）;^^^^^

失败：生成失败，出现异常。

• 其中：脚本"C：\flutter\flutter\packages\flutter_tools\gradle\flutter. gradle"行：1102
• 出了什么问题：任务"：app：compileFlutterBuildDebug"的执行失败。

进程"命令" C：\Flutter\flutter\bin\flutter.bat ""已完成，退出值为非零值1

• 尝试：使用--stacktrace选项运行以获取堆栈跟踪。使用--info或--debug选项运行以获取更多日志输出。使用--scan运行以获取完整的见解。
• 从https://help.gradle.org获取更多帮助

运行Gradle任务"assembleDebug"时，构建在1分27秒内失败... 90.2s异常：Gradle任务assembleDebug失败，退出代码为1
代码：

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}