How to exclude the dates from recurrence appointments in the Flutter Calendar

import 'package:flutter/material.dart';
import 'package:syncfusion_flutter_calendar/calendar.dart';
 
void main() => runApp(RecurrenceException());
 
class RecurrenceException extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: SafeArea(
          child: SfCalendar(
            view: CalendarView.week,
            dataSource: _getCalendarDataSource(),
          ),
        ),
      ),
    );
  }
 
  _AppointmentDataSource _getCalendarDataSource() {
    List<Appointment> appointments = <Appointment>[];
    DateTime exceptionDate = DateTime(2020, 12, 23);
    appointments.add(Appointment(
        startTime: DateTime.now(),
        endTime: DateTime.now().add(Duration(hours: 1)),
        subject: 'Meeting',
        color: Colors.pink,
        recurrenceRule:
        'FREQ=DAILY;COUNT=20',
        recurrenceExceptionDates: <DateTime>[exceptionDate]));
    )
    );
 
    return
    _AppointmentDataSource
    (
    appointments
    );
  }
}
 
class _AppointmentDataSource extends CalendarDataSource {
  _AppointmentDataSource(List<Appointment> source) {
    appointments = source;
  }
}