public function isValidEndDate(Campaign $campaign, \DateTime $endDate)
    {
        if($endDate != $campaign->getEndDate()){
            /*
             * While changing the campaign end date, has a later
             * Action been added by someone else?
             */
            /** @var Action $lastAction */
            $lastAction = $this->em->getRepository('CampaignChain\CoreBundle\Entity\Campaign')
                ->getLastAction($campaign);

            if($lastAction && $endDate < $lastAction->getStartDate()){
                return false;
            }
        }

        return true;
    }