Return a json dictionary representing this model.

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