[rules-users] Adhoc NullPointer exception in rule execution

Hi, folks, I'm using Drools 5.1, MVEL dialect, JDK 1.6 to build a OLTP system running on tomcat 6.0.28. the runtime environment is on a cloud virtual and node profile is relatively small. We've noticed below run time exceptions from prod since it's online from day one which is impacting transaction processing. However it is happening adhoc-ly. Here I have 1 question: 1. The yellow marked lines are actually java file compiled from DRL file. Why there is null pointer exception thrown from org.drools.common.DefaultAgenda.fireActivation? ERROR>2012-02-25 11:42:25,071 com.xxx.xxx.xxx.xxx[DefaultQuartzScheduler_Worker-3]: Rules run time error: org.drools.runtime.rule.ConsequenceException: rule: Match at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleExcept ion(DefaultConsequenceExceptionHandler.java:39) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:916) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:845) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1056) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.j ava:733) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.j ava:699) at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeS essionImpl.java:218) at com. xxx.xxx.xxx.xxx.xxx.xxx.xxx (SessionManager.java:94) at com. xxx.xxx.xxx.xxx.xxx.xxx.yyy(SessionManagerJob.java:17) at org.quartz.core.JobRunShell.run(JobRunShell.java:202) at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:525 ) Caused by: java.lang.NullPointerException at com.xxx.xxx.xxx.xxx.xxx.xxx.xxx(xxx.java:634) at com.xxx.xxx.xxx.xxx.xxx.yyy.yyy(yyy.java:227) at com.xxx.xxx.xxx.xxx.xxx.yyy.zzz(zzz.java:115) at com.xxx.xxx.xxx.xxx.xxx.yyy.ttt(ttt.java:83) at com.xxx.xxx.xxx.xxx.xxx.yyy.uuu(uuu.java:75) at com. com.xxx.xxx.xxx.xxx.xxx.yyy.vvv(vvv.java:9) at com. com.xxx.xxx.xxx.xxx.xxx.yyy.www(www.java:28) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:906) ... 9 more Best regards Abe