MapJoin.key() produces unusable Path object

I'm using MapJoin like this:

The em.createQuery(cq) call throws a NullPointerException:

The same code works fine on EclipseLink.

Seems that the problem is in the MapKeyHelpers.MapKeySource constructor, which calls the super constructor from AbstractPathSource with a null pathSource argument:

This way, the pathSource is initialized to null. Then, AbstractPathSource's getPathIdentifier() will always throw a NPE.