protected function getAclUsers()
    {
        $aclUsers = [];

        $userManagerServiceName = $this->container->getParameter('sonata.admin.security.acl_user_manager');
        if (null !== $userManagerServiceName && $this->has($userManagerServiceName)) {
            $userManager = $this->get($userManagerServiceName);

            if (method_exists($userManager, 'findUsers')) {
                $aclUsers = $userManager->findUsers();
            }
        }

        return \is_array($aclUsers) ? new \ArrayIterator($aclUsers) : $aclUsers;
    }