def validate(cls, job_config):
    """Validates relevant parameters.

    This method can validate fields which it deems relevant.

    Args:
      job_config: an instance of map_job.JobConfig.

    Raises:
      errors.BadWriterParamsError: required parameters are missing or invalid.
    """
    if job_config.output_writer_cls != cls:
      raise errors.BadWriterParamsError(
          "Expect output writer class %r, got %r." %
          (cls, job_config.output_writer_cls))