[rules-users] New in Drools, java.lang.NullPointerException at org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:967)

[Manuel Ortiz]

Hello all!

I am new in Drools but day by day, test by test, I think I get a bit more
knowledge of how the rule engine works from user point of view. I've been
adding rules to an alarm system, increasing the complexity and functionality
in several steps. Unfortunately in the last step I found the following
NullPointerException inside the rule engine...

java.lang.NullPointerException
at org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:967)
at org.drools.reteoo.AccumulateNode.modifyLeftTuple(AccumulateNode.java:329)
at
org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyChildLeftTuple(SingleLeftTupleSinkAdapter.java:239)
at
org.drools.reteoo.AccumulateNode.evaluateResultConstraints(AccumulateNode.java:640)
at org.drools.reteoo.AccumulateNode.assertObject(AccumulateNode.java:270)
at org.drools.reteoo.BetaNode.modifyObject(BetaNode.java:312)
at
org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:460)
at
org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:428)
at org.drools.reteoo.AlphaNode.modifyObject(AlphaNode.java:160)
at
org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:460)
at
org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:428)
at org.drools.reteoo.ObjectTypeNode.modifyObject(ObjectTypeNode.java:263)
at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:172)
at
org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1442)
at
org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1349)
at
org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:183)
at
org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:196)
at
es.simcasva.alarmas.rules.Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0.defaultConsequence(Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0.java:18)
at
es.simcasva.alarmas.rules.Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0DefaultConsequenceInvoker.evaluate(Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0DefaultConsequenceInvoker.java:44)
at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:917)
at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:856)
at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1071)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:785)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:751)
at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218)

I've been trying to find the problem, and found a strange interaction
between three rules that makes the null pointer to appear. The alarm system
has many rules now and it is difficult to simplify the scenario, so I just
would like to know what is the funcion of AccumulateNode object in order to
have an idea of the NullPointerException possible cause.

Can anyone help me?

Thank you in advance for your time.

Regards,

Manuel Ortiz.
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