I looked into the issue and it seems reported by users of the French locale. Without a reliable reproducer, which was not provided, I won't be able to do much about it. That said, is this issue really a blocker?
I want to point out that IZpack currently *crashes* on Java 9 and later and we have a fix already merged.
Even if we make *no other fixes* in 5.1.3, the users of IZPack will still be much better off with this release. Right now, they're just getting a crash and no explanation for it.
Can we please have a quick 5.1.3, to give users the benefits of the bugfixes we already have?