public static function getMembersOfGroup($nb_user_group) : CNabuUserGroupMemberList
    {
        if (is_numeric($nb_user_group_id = nb_getMixedValue($nb_user_group, 'nb_user_group_id'))) {
            $retval = CNabuUserGroupMember::buildObjectListFromSQL(
                'nb_user_id',
                "select ugm.* "
                . "from nb_user_group_member ugm, nb_user_group ug "
               . "where ugm.nb_user_group_id=ug.nb_user_group_id "
                 . "and ugm.nb_user_group_id=%group_id\$d",
                array(
                    'group_id' => $nb_user_group_id
                )
            );
        } else {
            $retval = new CNabuUserGroupMemberList();
        }

        return $retval;
    }