onLongPress property Null safety

CalendarLongPressCallback? onLongPress

Called whenever the SfCalendar elements long pressed on view.

The long-pressed date, appointments, and element details when the long-press action performed on element available in the CalendarLongPressDetails.

see also:

return Container(
     child: SfCalendar(
       view: CalendarView.week,
       onLongPress: (CalendarLongPressDetails details){
         DateTime date =!;
         dynamic appointments = details.appointments;
         CalendarElement view = details.targetElement;


final CalendarLongPressCallback? onLongPress;