docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'custom_language_model'
                    ) and self.custom_language_model is not None:
              _dict['custom_language_model'] = self.custom_language_model
          if hasattr(self, 'speaker_labels') and self.speaker_labels is not None:
              _dict['speaker_labels'] = self.speaker_labels
          return _dict