I get a
not-null property references a null or transient value exception,
which I guess is quite common. But the log file does not tell me which value is null. of couse it could be the object being saved or any of the reachabe objects. so there is quite a lot of possible offenders.

can't I get hibernate to dump out into log4j exactly which one is null?

ok, it was a wrong call of session.save() instead of update().

setting overall log4j level to debug helped to point to the id of the object being NULL, which got my attention.

I was able to dump out the exact sql commands using p6spy, in case any body else is searching how to do this. That really helped debugging all around.