将列表<；Events>；从Flutter 应用程序中的函数传回EventLoader属性时出错

我正在try 在Ffltter应用程序中的TABLE_CALENLER小部件上填充事件，但在使用TABLE_CALLER小部件的Events和eventsLoader:属性时遇到了问题.

我已经计算出，如果我使用2 for循环，我可以填充类型事件的列表，List，并将其传递回eventsLoader，但我收到了一个我不理解的错误.

以下是我使用的代码:

      eventLoader: (day) {
        return _getEventsForDay(day, events);  <<< ERROR HERE
      },

  List<Events>? _getEventsForDay(DateTime day, [List<Events>? events]) {
    final int today = day.day;
    final int nbrEvents = events!.length;

    for (Events allEvent in events) {
      if (day.year == allEvent.eventDate!.year &&
          day.month == allEvent.eventDate!.month &&
          day.day == allEvent.eventDate!.day) {
        // fill this list with all the events associated
        //with the given day and pass the list back
        late final List<Events> listDayEvents = [];
        for (Events dayEvents in events) {
          if (day.year == allEvent.eventDate!.year &&
              day.month == allEvent.eventDate!.month &&
              day.day == allEvent.eventDate!.day) {
            listDayEvents.add(allEvent);
          }
        }
        return listDayEvents;
      }
      List<Events> emptyList = [];
      return emptyList;
    }
  }

我在EventsLoader:属性上收到的错误如下:

The return type 'List<Events>?' isn't a 'List<_>', as required by the closure's context.dartreturn_of_invalid_type_from_closure
List<Events>? _getEventsForDay(DateTime day, [List<Events>? events])
Type: List<Events>? Function(DateTime, [List<Events>?])

package:deal_diligence/screens/appointment_calendar.dart

我不理解这个错误消息，因为我返回的是List类型.

这是Events类.我从Firebase集合中获取事件，并且每个事件都有Events类中的数据元素，那么我传递的数据类型是否错误？

class Events {
  String? id;
  String? eventName;
  DateTime? eventStartTime;
  String? eventDuration;
  DateTime? eventDate;
  String? eventDescription;
  String? userId;
  String? companyId;

这里是table_calendar widget的文档链接

我做错了什么？请帮帮忙. 谢谢