public static List <Appointment> GetParticipantsWantedAppointments(List <User> selectedUsers, AppointmentDatabase appointmentDatabase, Appointment selectedAppointment)
        {
            List <Appointment> selectedUsersAppointments = new List <Appointment>();

            if (selectedUsers != null && appointmentDatabase != null)
            {
                foreach (User user in selectedUsers)
                {
                    selectedUsersAppointments.AddRange(appointmentDatabase.GetSelectedUserWantedAppointments(user, selectedAppointment));
                }
            }

            return(selectedUsersAppointments);
        }