Users, I am trying to follow this example in the main drools documentation: http://docs.jboss.org/drools/release/5.4.0.Final/drools-fusion-docs/html_... I have a simple rule that listens for an event, and provide an average over a 3-event sliding window. I see 2 issues. _DRL = "rule myRule\n" _DRL += "when\n" _DRL += "> $avg: Number() from accumulate (\n" _DRL += "> DatapointProxy( key == 'testUsedMemPct', $val : valueAsDouble ) over window:length( 3 ), \n" _DRL += "> average( $val ) )\n" _DRL += "then\n" _DRL += " handleRule( rule, ruleResource, userdata, $avg );\n" _DRL += "end\n" 1) my rule evaluates try for every event, and gives me the value of the event vs the avg. So if i send 50, 60, 70, my handleRule function is a called 3 times with new event array(java.lang.Object, [50.0]), array(java.lang.Object, [60.0]), array(java.lang.Object, [70.0]) 2) On the 4th event, I get the following NPE (includes JSON of target object): Msg: {"DatapointProxy":{"value":"80","modTime":1362148018519,"uuid":"87163fc1-b072-4311-8cb4-b604d6d874ed","ownerUUID":"90d9d3d1-dd57-42b7-beba-4927c5551409","generatorUUID":"a8dfd038-c7a6-4317-8bf5-7911d7dbb759","key":"testUsedMemPct","name":"Test Mem Value","managerUUID":"3beb7ead-f351-42a3-a4a4-38425b061a5a"}} Error: java.lang.NullPointerException java.lang.NullPointerException at org.drools.rule.SlidingLengthWindow.assertFact(SlidingLengthWindow.java:115) at org.drools.rule.BehaviorManager.assertFact(BehaviorManager.java:94) at org.drools.reteoo.WindowNode.assertObject(WindowNode.java:167) at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382) at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235) at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:350) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847) at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:269) at com.codemettle.sherpa.cam.jms.JMSMessageListenerForDrools.injectEvent(JMSMessageListenerForDrools.java:128) at com.codemettle.sherpa.cam.jms.JMSMessageListenerForDrools.onMessage(JMSMessageListenerForDrools.java:105) at org.apache.activemq.ActiveMQMessageConsumer.dispatch(ActiveMQMessageConsumer.java:1321) at org.apache.activemq.ActiveMQSessionExecutor.dispatch(ActiveMQSessionExecutor.java:131) at org.apache.activemq.ActiveMQSessionExecutor.iterate(ActiveMQSessionExecutor.java:202) at org.apache.activemq.thread.PooledTaskRunner.runTask(PooledTaskRunner.java:129) at org.apache.activemq.thread.PooledTaskRunner$1.run(PooledTaskRunner.java:47) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:662) I would appreciate some help figuring out what the issue is. Is there something fishy in my rule? I thank you in advance for your consideration and help -- View this message in context: http://drools.46999.n3.nabble.com/Accumulate-Over-window-average-NullPoin... Sent from the Drools: User forum mailing list archive at Nabble.com.