flutter - 启用不可为空功能后，由于其类型，参数不能具有 null 值

Question

class MyPage extends StatelessWidget {
  MyPage({Key key}) : super(key: key); // error in this line

  @override
  Widget build(BuildContext context) => Container();
}

这段代码之前没有错误，但现在它显示给我

key can't have a value of null because of its type