docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self,
                     'conversation_id') and self.conversation_id is not None:
              _dict['conversation_id'] = self.conversation_id
          if hasattr(self, 'system') and self.system is not None:
              _dict['system'] = self.system._to_dict()
          if hasattr(self, 'metadata') and self.metadata is not None:
              _dict['metadata'] = self.metadata._to_dict()
          if hasattr(self, '_additionalProperties'):
              for _key in self._additionalProperties:
                  _value = getattr(self, _key, None)
                  if _value is not None:
                      _dict[_key] = _value
          return _dict