public async Task <CustomError> AddHoliday(string name, string description, string destination, DateTime holidayDepartureDate)
{
Holiday holiday = new Holiday(name, description, destination, holidayDepartureDate);
(Holiday h, CustomError c) = await HolidayService.AddHoliday(holiday);
if (h.ID >= 0 && c.Message == null)
{
Holidays.Add(h);
}
return(c);
}