Here's my reproduced steps:
1). start the domain
2). login the admin console
3). Access to the Avaliable Service page under default-config.
4). Type the Web Conatiner Availability page and save the default setting
5). Error in saving the default setting
6). The NPE will be thrown to the server.log, here's the stacktrace:
Once the NPE was thrown out, All of the operation related to the Availability Service page are useless. So I think it is a critical issue need to be fix as soon as possible.