code: def _check_load_existing_object(self, object_type, id_field_name, operation='update'):
          # type: (str, str, str) -> None
          
          self._check_existing_object(object_type, id_field_name)
          if not self._load_from_hdx(object_type, self.data[id_field_name]):
              raise HDXError('No existing %s to %s!' % (object_type, operation))
docs: Check metadata exists and contains HDX object identifier, and if so load HDX object
  
          Args:
              object_type (str): Description of HDX object type (for messages)
              id_field_name (str): Name of field containing HDX object identifier
              operation (str): Operation to report if error. Defaults to update.
  
          Returns:
              None