code: def add_key_value(self, key, value):
          
          key = self._metadata_map.get(key, key)
          if key in ['dateAdded', 'eventDate', 'firstSeen', 'publishDate']:
              self._group_data[key] = self._utils.format_datetime(
                  value, date_format='%Y-%m-%dT%H:%M:%SZ'
              )
          elif key == 'file_content':
              # file content arg is not part of Group JSON
              pass
          else:
              self._group_data[key] = value
docs: Add custom field to Group object.
  
          .. note:: The key must be the exact name required by the batch schema.
  
          Example::
  
              document = tcex.batch.group('Document', 'My Document')
              document.add_key_value('fileName', 'something.pdf')
  
          Args:
              key (str): The field key to add to the JSON batch data.
              value (str): The field value to add to the JSON batch data.