public static function get_user_version_acceptance($userid, $versionid, $acceptances = null) {
        if (empty($acceptances)) {
            $acceptances = static::get_user_acceptances($userid, $versionid);
        }
        if (array_key_exists($versionid, $acceptances)) {
            // The policy version has ever been accepted.
            return $acceptances[$versionid];
        }

        return null;
    }