code: def _fill_from_default(self, default_job_config):
          
          if self._job_type != default_job_config._job_type:
              raise TypeError(
                  "attempted to merge two incompatible job types: "
                  + repr(self._job_type)
                  + ", "
                  + repr(default_job_config._job_type)
              )
  
          new_job_config = self.__class__()
  
          default_job_properties = copy.deepcopy(default_job_config._properties)
          for key in self._properties:
              if key != self._job_type:
                  default_job_properties[key] = self._properties[key]
  
          default_job_properties[self._job_type].update(self._properties[self._job_type])
          new_job_config._properties = default_job_properties
  
          return new_job_config
docs: Merge this job config with a default job config.
  
          The keys in this object take precedence over the keys in the default
          config. The merge is done at the top-level as well as for keys one
          level below the job type.
  
          Arguments:
              default_job_config (google.cloud.bigquery.job._JobConfig):
                  The default job config that will be used to fill in self.
  
          Returns:
              google.cloud.bigquery.job._JobConfig A new (merged) job config.