docs: @Override
      public ModelService getModelService(String serviceName){
          ModelService service = null;
          if (getCache().isCached(serviceName)) {
              service = getCache().getService(serviceName);
          } else {
              service= this.getDirectoryServiceClient().getService(serviceName, watcher);
              if(service != null){
                  getCache().putService(serviceName, service);
              }
          }
          return service;
      }