Granted the folks I know using Maven enhancing plugin have a very simple domain model they need to enhance it is possible they just got lucky. I asked Luis to take a look. That being said a lot of the issue we are seeing reported are related to (1) using Maven and (2) using Windows. None of us use Windows, so we for sure lose coverage there. As for Maven, well I think my thoughts on Maven are generally well-known, so I won't get into it here. Suffice to say, Maven tooling is not where I will be expending my energies; if community wants to help support that great. That's what happened for the initial Maven plugin contribution. So we will certainly look into the Maven-plugin PRs.

The Enhancer does add any classpath to the Javassist ClassPool (which is how Javassist resolves Class references). IIUC based on a comment in one of the Maven plugin PRs, the problem is again Maven and its utter awesomeness essentially not allowing the project being built to be part of the classpath for the plugin execution. It had a suggestion. Luis will take a look. There are other ways to enhance classes other than relying on this Maven plugin, so to me working in Maven is not a blocker.

As far as the NPE... ultimately not every class should have to be enhanced. For some capabilities I think that would be needed (like bi-directional management), but just talking about in general. That said, I have a hard time groking how line 238 you pointed out can lead to a NPE. Hard to say, since I have not see a bug report for it.