Long time ago I described my problem with getLastPerformer() xpatch function. Content of this artice you can find here: http://my-java-planet.blogspot.com/2012/11/bpm-getlastperformer-issue-error-in.html
Yesterday I encountered this problem once again. And again, I forget cause of this issue. After some googling, I found my own blog post regarding getLastPerformer().
Fortunatelly, today I know, that you can't use bpm.getLastPerformer() outside of Human Taskflow task (the only place I've seen getLastPerformer() method invoked successfully is from inside the human task's assignment tab), so I can share this knowledge. And this is the whole mystery:)
