public function addUsersToGroup(Group $group, array $users)
    {
        $addedUsers = [];

        if (!$this->validateAddUsersToGroup($users, $group)) {
            throw new Exception\AddRoleException();
        }

        foreach ($users as $user) {
            if (!$group->containsUser($user)) {
                $addedUsers[] = $user;
                $group->addUser($user);
                $this->eventDispatcher->dispatch('log', 'Log\LogGroupAddUser', [$group, $user]);
            }
        }

        $this->om->persist($group);
        $this->om->flush();

        return $addedUsers;
    }