public function WaitingListRegistrationForm()
    {
        if (
            $this->owner->Tickets()->count()
            && $this->owner->getTicketsSoldOut()
            && !$this->owner->getEventExpired()
        ) {
            return new WaitingListRegistrationForm($this->owner, 'WaitingListRegistrationForm');
        } else {
            return null;
        }
    }