code: func cfgIP(cfg *conf.ConfigFile, section, option string) (net.IP, error) {
  	ipStr := cfgOpt(cfg, section, option)
  	if ipStr == "" {
  		return nil, nil
  	}
  	ip := net.ParseIP(ipStr)
  	if ip == nil {
  		return nil, fmt.Errorf("%s: %q is not a valid IP address", option, ipStr)
  	}
  	return ip, nil
  }
docs: // cfgIP returns configuration option from the specified section, as an IP
  // address. If the option does not exist or is blank, a nil IP is returned.