public ActionResult <IEnumerable <User> > GetAbsent(DateTime date)
        {
            IEnumerable <User> users = _customDayRepository.GetAbsentUsersForDay(date).ToList();

            if (users == null || !users.Any()) // this condition was added because even if nothing matches the predicate a list with 0 items is returned
                                               // variable == is always false
            {
                return(NotFound());
            }
            else
            {
                return(Ok(users));
            }
        }