I've encountered a NPE in TruthMaintananceSystem:304 on retractions of
tracked facts (because getLogicalDependencies() returns null).

I hunted it down to DefaultKnowledgeHelper::setActivation() method. A
comment there says that this was added to resolve the JBRULES-2558
bug.

My attempt to fix it is attached - instead of removing the list of
logical dependencies, I instead track re-additions and then remove
everything else.