Flutter Local Notification onSelectNotification 函数参数类型无法分配

如何解决Flutter Local Notification onSelectNotification 函数参数类型无法分配

我正在为我的应用程序使用 Local Notifications，并且我正在尝试设置 onSelectNotification，但我无法使其工作。我就是这样init：

 Future initialize() async {
    FlutterlocalnotificationsPlugin FlutterlocalnotificationsPlugin =
        FlutterlocalnotificationsPlugin();

    AndroidInitializationSettings androidInitializationSettings =
        AndroidInitializationSettings('app_icon');

    IOSInitializationSettings iosInitializationSettings =
        IOSInitializationSettings();

    final InitializationSettings initializationSettings =
        InitializationSettings(
            android: androidInitializationSettings,iOS: iosInitializationSettings);

    await FlutterlocalnotificationsPlugin.initialize(
      initializationSettings,onSelectNotification: onSelectNotification
    );
  }

还有我的onSelectNotification：

  Future onSelectNotification(String payload) async {
    print(payload);
  }

但 Flutter 正在抱怨：

无法将参数类型“Future Function(String)”分配给参数类型“Future Function(String?)?”。

我在文档中找不到任何关于此的内容，其他地方也找不到。我想念她什么？