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