Return a json dictionary representing this model.

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