code: def _to_dict(self):
          
          _dict = {}
          if hasattr(self, 'tones') and self.tones is not None:
              _dict['tones'] = [x._to_dict() for x in self.tones]
          if hasattr(self,
                     'tone_categories') and self.tone_categories is not None:
              _dict['tone_categories'] = [
                  x._to_dict() for x in self.tone_categories
              ]
          if hasattr(self, 'warning') and self.warning is not None:
              _dict['warning'] = self.warning
          return _dict
docs: Return a json dictionary representing this model.