Return a json dictionary representing this model.

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