public function cancel($hostUserId, $appointmentId)
{
if ($this->haveMissingUser($hostUserId)) {
throw new Cv\Exceptions\MissingModelException();
}
$appointment = Chatroom::findOrDie($appointmentId);
if (is_null($appointment)) {
throw new Cv\Exceptions\MissingModelException();
}
// I don't know cancel processes
}
