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