Hi Björn, do I understand correctly that if you place a bean in your deployment or remove the ui:debug tag the problem is gone? Would it be possible to share your minimal project?

It seems that Weld is not started. In Weld SE/Servlet there is an optimization - empty bean archives are ignored. And if there are no CDI bean archives found in the deployment then Weld initialization is completely skipped. You should see a similar message in the log:

Weld initialization skipped - no bean archive found

In other words, if your deployment is empty then the exception is expected.