Return a json dictionary representing this model.

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