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