docs: public ModelMetadataKey getMetadataKey(String keyName){
          HttpResponse result = invoker.invoke("/metadatakey/" + keyName , null, HttpMethod.GET);
  
          if (result.getHttpCode() != HTTP_OK) {
             throw new ServiceException(ErrorCode.REMOTE_DIRECTORY_SERVER_ERROR,
                      "HTTP Code is not OK, code=%s", result.getHttpCode());
          }
  
          ModelMetadataKey key = _deserialize(
                      result.getRetBody(), ModelMetadataKey.class);
  
          return key;
      }