@Override
public void register(User user, Lva appointment, User responsibleUser) throws RegisterPeriodOverException, AlreadyRegisteredException, MaximumMemberCountExceededException, RequirementsNotFullfilledException, AppointmentNotFoundException, NotAllowedException {
Lva real = getRealAppointment(appointment);
if (real == null || real.isDeleted()) {
throw new AppointmentNotFoundException();
}
if (!(user instanceof Student)) {
throw new IllegalArgumentException("Only students can register to a Lva!");
}