Return a json dictionary representing this model.

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