Where to download openhab-helper-libraries for OH 3.0

@5iver I been looking at that for some time but I haven’t been able to solve.
Is this suposed to work with Java 11? I found that thread, but it’s not clear to me if that is expected to work or not.

Debuguing and putting a breakpoint on exceptions I’ve been able to catch that:

That seems strange, because in some way it’s detected if it’s tried to be added, isn’t it?