code: def fill_null_values(self):
          
          if not self.Model:
              log.info("%s has no model defined" % self.__class__.__name__)
              return
  
          empty_values = self.Model.get_null_values()
          for field, value in empty_values.items():
              if field not in self._json_params:
                  self._json_params[field] = value
docs: Fill missing model fields in JSON with {key: null value}.
  
          Only run for PUT requests.