When upgrading to drools 5, valid drools 4 xml rules do not work. Drools just throws an unhelpful null pointer exception. What can the problem be?
A:
The problem is that Drools 5 changed the namespace. Replace xmlns="http://drools.org/drools-4.0" with xmlns="http://drools.org/drools-5.0" and at least for simple rules that is all you need.
I hope that helps save someone the headache I just got dealing with this undocumented change.
Yishai
2010-07-22 23:22:47