docs: @Override
      public String[] findMemberGroupKeys(IEntityGroup group) throws GroupsException {
  
          if (isTreeRefreshRequired()) {
              refreshTree();
          }
  
          log.debug("Invoking findMemberGroupKeys() for group:  {}", group.getLocalKey());
  
          List<String> rslt = new ArrayList<>();
          for (Iterator it = findMemberGroups(group); it.hasNext(); ) {
              IEntityGroup g = (IEntityGroup) it.next();
              // Return composite keys here...
              rslt.add(g.getKey());
          }
  
          return rslt.toArray(new String[rslt.size()]);
      }