code: func RawCombinedOutput(args ...string) error {
  	if output, err := Raw(args...); err != nil || len(output) != 0 {
  		return fmt.Errorf("%s (%v)", string(output), err)
  	}
  	return nil
  }
docs: // RawCombinedOutput internally calls the Raw function and returns a non nil
  // error if Raw returned a non nil error or a non empty output