docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'age') and self.age is not None:
              _dict['age'] = self.age._to_dict()
          if hasattr(self, 'gender') and self.gender is not None:
              _dict['gender'] = self.gender._to_dict()
          if hasattr(self, 'face_location') and self.face_location is not None:
              _dict['face_location'] = self.face_location._to_dict()
          return _dict