NPE in BehaviorJobContextTimerOutputMarshaller.write

Caused by: java.lang.NullPointerException
	at org.drools.rule.SlidingTimeWindow$BehaviorJobContextTimerOutputMarshaller.write(SlidingTimeWindow.java:298)
	at org.drools.marshalling.impl.OutputMarshaller.writeTimers(OutputMarshaller.java:1105)
	at org.drools.marshalling.impl.OutputMarshaller.writeSession(OutputMarshaller.java:172)
	at org.drools.marshalling.impl.DefaultMarshaller.marshall(DefaultMarshaller.java:142)
	at org.drools.marshalling.impl.DefaultMarshaller.marshall(DefaultMarshaller.java:125)
	at org.drools.persistence.SessionMarshallingHelper.getSnapshot(SessionMarshallingHelper.java:72)
	at org.drools.persistence.info.SessionInfo.update(SessionInfo.java:84)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.hibernate.ejb.event.BeanCallback.invoke(BeanCallback.java:23)
	at org.hibernate.ejb.event.EntityCallbackHandler.callback(EntityCallbackHandler.java:80)
	at org.hibernate.ejb.event.EntityCallbackHandler.preUpdate(EntityCallbackHandler.java:65)
	at org.hibernate.ejb.event.EJB3FlushEntityEventListener.invokeInterceptor(EJB3FlushEntityEventListener.java:41)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.handleInterception(DefaultFlushEntityEventListener.java:330)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.scheduleUpdate(DefaultFlushEntityEventListener.java:270)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:151)
	at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)
	at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
	at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:49)
	at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1028)
	at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:366)
	at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
	at org.hibernate.ejb.TransactionImpl.commit(TransactionImpl.java:54)
	... 34 more