[DROOLS-376] avoid NPE on JPAKnowledgeService.loadStatefulKnowledgeSession() when Collection is modified
(cherry picked from commit 384b22588c9b71c7e333eb57844216f7a0765234)
[DROOLS-376] avoid NPE on JPAKnowledgeService.loadStatefulKnowledgeSession() when Collection is modified
(cherry picked from commit a45a1189facc30952831c90c220fb3fc4c9878a7)