public void RemoveAppointment(int appointmentId)
        {
            lock (_lockingObject)
            {
                _persistable.RemoveAppointment(appointmentId);
                Appointment appointment = _appointments.Find(appointment1 => appointment1.Id == appointmentId);

                _updateAppointmentNotification.AppointmentDeletedNotification(appointment);
                _appointments.Remove(appointment);
            }

            AppointmentsChangedEventHandler?.Invoke(appointmentId, EventArgs.Empty);
        }