code: @Trivial
      private Root keepCheckPointForReposOnly(Root searchDO, String reposId) {
          Root retDO = new Root();
          Map<String, Control> ctrlsMap = ControlsHelper.getControlMap(searchDO);
          ChangeControl changeCtrl = (ChangeControl) ctrlsMap.get(DO_CHANGE_CONTROL);
          ChangeControl returnChangeControl = new ChangeControl();
          CheckPointType returnCheckPoint = new CheckPointType();
          returnChangeControl.getCheckPoint().add(returnCheckPoint);
          retDO.getControls().add(returnChangeControl);
          List<CheckPointType> checkPointList = changeCtrl.getCheckPoint();
          if (checkPointList != null) {
              for (CheckPointType checkPointDO : checkPointList) {
                  if (checkPointDO.getRepositoryId().equals(reposId)) {
                      returnCheckPoint.setRepositoryCheckPoint(checkPointDO.getRepositoryCheckPoint());
                      returnCheckPoint.setRepositoryId(checkPointDO.getRepositoryId());
                  }
              }
          }
          return retDO;
      }
docs: This method is invoked by searchImpl() to make sure that each
  adapter receives only its corresponding checkpoint in the change
  control.
  
  @param searchDO Input search DataObject
  @param reposId Identifier for the repository whose checkpoint needs to be retained
  @return Object for search containing checkpoint corresponding to reposId only