public function sendMessage(Announcement $announcement, array $users = [])
    {
        $message = $this->getMessage($announcement, $users);

        $announcementSend = new AnnouncementSend();
        $data = $message;
        $data['receivers'] = array_map(function (User $receiver) {
            return $receiver->getUsername();
        }, $message['receivers']);
        $data['sender'] = $message['sender']->getUsername();
        $announcementSend->setAnnouncement($announcement);
        $announcementSend->setData($data);
        $this->om->persist($announcementSend);
        $this->om->flush();

        $this->eventDispatcher->dispatch(
            'claroline_message_sending_to_users',
            'SendMessage',
            [
                $message['sender'],
                $message['content'],
                $message['object'],
                null,
                $message['receivers'],
            ]
        );
    }