AbstractServerConfig.toIPv6URLFormat throws java.net.UnknownHostException

After applying the changes for IPv6 support, the AbstractServerConfig::toIPv6URLFormat method does a InetAddress.getByName(host) call that can throws UnknownHostException if the webserviceHost in the configuration can't be lookup.
This needs to be changed or at least surrounded by a try-catch block as it's not robust (to be honest nothing even prevents the user from wanting a fancy hostname in there).