Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'from_') and self.from_ is not None:
            _dict['from'] = self.from_
        if hasattr(self, 'to') and self.to is not None:
            _dict['to'] = self.to
        if hasattr(self, 'speaker') and self.speaker is not None:
            _dict['speaker'] = self.speaker
        if hasattr(self, 'confidence') and self.confidence is not None:
            _dict['confidence'] = self.confidence
        if hasattr(self, 'final_results') and self.final_results is not None:
            _dict['final'] = self.final_results
        return _dict