Created attachment 691413 [details]
Screenshot

If you don't have any firewall installed (susefirewall, firewalld) and you
start Yast Firewall, it should ask you to install susefirewall (or firewalld),
but it only reports that

  YaST cannot continue the configuration without
  installing the required packages

                   [ OK ]

And when you hit the OK button, it exits immediately.
There is no question whether Yast should install any additional package.

This is maybe related to a feature that we can now also configure
firewalld. BTW, this bug is probably also in SLE 12 SP2 (but I haven't
tested it there), just the code is the same.