I'm getting this same exception. I create 5 instances of a process. Mid-point in the process I have a timer, and things are run/persisted properly until the timer is reached. At this point control is returned to the caller, which waits for some time until re-aquiring the session instances (via JPAKnowledgeService.loadStatefulKnowledgeSession(w, x, y, z)) and fireUntilHalt() is called on the ksession. At this point, an intermittent # of my remaining process instances will execute properly (maybe 2 out of 5), and the remaining fail with the following exception:
Hibernate: select processins0_.InstanceId as InstanceId121_0_, processins0_.lastModificationDate as lastModi2_121_0_, processins0_.lastReadDate as lastRead3_121_0_, processins0_.processId as processId121_0_, processins0_.processInstanceByteArray as processI5_121_0_, processins0_.startDate as startDate121_0_, processins0_.state as state121_0_, processins0_.OPTLOCK as OPTLOCK121_0_ from ProcessInstanceInfo processins0_ where processins0_.InstanceId=?
org.drools.RuntimeDroolsException: Unexpected exception executing action org.jbpm.process.instance.event.DefaultSignalManager$SignalProcessInstanceAction@3f1dae99
at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:996)
at org.drools.impl.StatefulKnowledgeSessionImpl.executeQueuedActions(StatefulKnowledgeSessionImpl.java:845)
at org.jbpm.process.instance.event.DefaultSignalManager.signalEvent(DefaultSignalManager.java:89)
at org.jbpm.process.instance.timer.TimerManager$ProcessJob.execute(TimerManager.java:164)
at org.drools.time.impl.JDKTimerService$JDKCallableJob.call(JDKTimerService.java:151)
at org.drools.persistence.jpa.JpaJDKTimerService$JpaJDKCallableJob.internalCall(JpaJDKTimerService.java:80)
at org.drools.persistence.jpa.JpaJDKTimerService$JpaJDKCallableJob.access$100(JpaJDKTimerService.java:63)
at org.drools.persistence.jpa.JpaJDKTimerService$JDKCallableJobCommand.execute(JpaJDKTimerService.java:96)
at org.drools.persistence.jpa.JpaJDKTimerService$JDKCallableJobCommand.execute(JpaJDKTimerService.java:84)
at org.drools.persistence.SingleSessionCommandService.execute(SingleSessionCommandService.java:292)
at org.drools.persistence.jpa.JpaJDKTimerService$JpaJDKCallableJob.call(JpaJDKTimerService.java:75)
at org.drools.persistence.jpa.JpaJDKTimerService$JpaJDKCallableJob.call(JpaJDKTimerService.java:63)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.getEntityManager(JPAWorkingMemoryDbLogger.java:131)
at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.addNodeExitLog(JPAWorkingMemoryDbLogger.java:118)
at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.logEventCreated(JPAWorkingMemoryDbLogger.java:80)
at org.drools.audit.WorkingMemoryLogger.filterLogEvent(WorkingMemoryLogger.java:196)
at org.drools.audit.WorkingMemoryLogger.beforeNodeLeft(WorkingMemoryLogger.java:506)
at org.drools.event.ProcessEventSupport.fireBeforeNodeLeft(ProcessEventSupport.java:112)
at org.jbpm.workflow.instance.impl.NodeInstanceImpl.triggerConnection(NodeInstanceImpl.java:162)
at org.jbpm.workflow.instance.impl.NodeInstanceImpl.triggerCompleted(NodeInstanceImpl.java:150)
at org.jbpm.workflow.instance.impl.ExtendedNodeInstanceImpl.triggerCompleted(ExtendedNodeInstanceImpl.java:47)
at org.jbpm.workflow.instance.node.StateBasedNodeInstance.triggerCompleted(StateBasedNodeInstance.java:162)
at org.jbpm.workflow.instance.node.TimerNodeInstance.triggerCompleted(TimerNodeInstance.java:135)
at org.jbpm.workflow.instance.node.TimerNodeInstance.signalEvent(TimerNodeInstance.java:125)
at org.jbpm.workflow.instance.impl.WorkflowProcessInstanceImpl.signalEvent(WorkflowProcessInstanceImpl.java:333)
at org.jbpm.process.instance.event.DefaultSignalManager$SignalProcessInstanceAction.execute(DefaultSignalManager.java:117)
at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:994)
... 18 more