Return a json dictionary representing this model.

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