public void update(final Reservation reservation) {

    if (!reservationRepository.existsById(reservation.getId())) {
      throw new GuestNotFoundException();
    }

    reservationRepository.update(reservation);
  }
 public Reservation findById(final Long id) {
   final Reservation reservation = reservationRepository.findById(id);
   if (reservation == null) {
     throw new GuestNotFoundException();
   }
   return reservation;
 }
 public void remove(final Reservation reservation) {
   reservationRepository.remove(reservation, reservation.getId());
 }
 public List<Reservation> fyndAll() {
   return reservationRepository.findAll("checkinDate");
 }
 public Reservation add(final Reservation reservation) {
   return reservationRepository.add(reservation);
 }