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