code: public static String unresolvedHostToNormalizedString(String host) {
  		// Return loopback interface address if host is null
  		// This represents the behavior of {@code InetAddress.getByName } and RFC 3330
  		if (host == null) {
  			host = InetAddress.getLoopbackAddress().getHostAddress();
  		} else {
  			host = host.trim().toLowerCase();
  		}
  
  		// normalize and valid address
  		if (IPAddressUtil.isIPv6LiteralAddress(host)) {
  			byte[] ipV6Address = IPAddressUtil.textToNumericFormatV6(host);
  			host = getIPv6UrlRepresentation(ipV6Address);
  		} else if (!IPAddressUtil.isIPv4LiteralAddress(host)) {
  			try {
  				// We don't allow these in hostnames
  				Preconditions.checkArgument(!host.startsWith("."));
  				Preconditions.checkArgument(!host.endsWith("."));
  				Preconditions.checkArgument(!host.contains(":"));
  			} catch (Exception e) {
  				throw new IllegalConfigurationException("The configured hostname is not valid", e);
  			}
  		}
  
  		return host;
  	}
docs: Returns an address in a normalized format for Akka.
  When an IPv6 address is specified, it normalizes the IPv6 address to avoid
  complications with the exact URL match policy of Akka.
  @param host The hostname, IPv4 or IPv6 address
  @return host which will be normalized if it is an IPv6 address