code: def load_unknown_fields(self, data, original_data):
          
          if isinstance(original_data, list):
              for elem in original_data:
                  self.load_unknown_fields(data, elem)
          else:
              for key, value in original_data.items():
                  if key not in data:
                      data[key] = value
          return data
docs: Check for unknown keys.