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