During development of our Drools rule base I had a case where a rule compiled fine, but at runtime a NPE is thrown by MVEL when applying the predicate (LHS) because the Coverage.vehicleSupplement attribute was NULL. I had expected the NPE to be returned to my calling java program so that my try/catch could address the issue. However, the exception was sent to System.err and the rule was simply skipped. First, is the the default behavior in Drools for Exceptions thrown from the LHS? If so, can it be overridden to actually return the exception? rule "BR--UM Stacked Coverage" agenda-group "BR_Change" dialect "mvel" when coverage : Coverage( vehicleSupplement.stackable == true , coverageCode == "UDCSL") vehicle : Vehicle( unitAtRiskNumber : unitAtRiskNumber) Policy( state == "NM" ) then WorkItemReason fact0 = new WorkItemReason(); fact0.setType( "Policy" ); fact0.setReason( "6408: UM/UDM stacking change" ); fact0.setAddBookmark( "VE" ); fact0.setAddBookmarkUnit( unitAtRiskNumber ); insertLogical(fact0 ); end *Here is the stacktrace from my console:* WARNING: java.lang.RuntimeException: cannot invoke getter: getVehicleSupplement [declr.class: com.fbfs.pc.ecd.model.Coverage; act.class: com.fbfs.pc.ecd.model.Coverage] (see trace) at org.mvel2.optimizers.impl.refl.nodes.GetterAccessor.getValue(GetterAccessor.java:74) at org.mvel2.ast.ASTNode.getReducedValueAccelerated(ASTNode.java:106) at org.mvel2.MVELRuntime.execute(MVELRuntime.java:87) at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:122) at org.mvel2.MVEL.executeExpression(MVEL.java:954) at org.drools.base.extractors.MVELClassFieldReader.getValue(MVELClassFieldReader.java:100) at org.drools.base.extractors.BaseObjectClassFieldReader.isNullValue(BaseObjectClassFieldReader.java:179) at org.drools.base.evaluators.EqualityEvaluatorsDefinition$BooleanEqualEvaluator.evaluate(EqualityEvaluatorsDefinition.java:555) at org.drools.rule.LiteralRestriction.isAllowed(LiteralRestriction.java:87) at org.drools.rule.LiteralConstraint.isAllowed(LiteralConstraint.java:109) at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:130) at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:458) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:386) at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:215) at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:244) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:330) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:291) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:886) at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:180) at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:174) at PolicyDefinitionRules.Rule_policyDefinition_UnitAtRiskCoverage.defaultConsequence(Rule_policyDefinition_UnitAtRiskCoverage.java:8) at PolicyDefinitionRules.Rule_policyDefinition_UnitAtRiskCoverageDefaultConsequenceInvoker.evaluate(Unknown Source) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1029) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1251) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:708) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:672) at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218) at com.fbfs.pc.rulesengine.controller.RulesEngine.runRulesEngine(RulesEngine.java:318) My expectation that Exceptions thrown from the consequence (RHS) are returned to the calling program was confirmed when I added the following 2 lines to a rule that was not experiencing the above issue: String myString = null; System.out.println(myString.trim()); Is there any good documentation on Drools exception handling? Current configuration is Drools 5.3.0, MVEL 2.1.0, Glassfish 2.1 -- View this message in context: http://drools.46999.n3.nabble.com/NPE-from-LHS-of-rule-is-not-returned-by... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users

No, the NPE is not thrown up to my java class that calls fireAllRules(), that is the problem. I'm hoping someone who has lots of experience with Exception Handing in LHS of Drools rules can chime in here and say whether this is the default behavior for Drools. If not, what might be causing the exception to be sent to System.err. -- View this message in context: http://drools.46999.n3.nabble.com/NPE-from-LHS-of-rule-is-not-returned-by... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users

I understand that I cannot expect to catch NPE in my calling java program. I am actually catching java.lang.Exception. I simply continued to call it an NPE because that was the true issue. My issue can easily be broadened to apply to any RuntimeException thrown from LHS. -- View this message in context: http://drools.46999.n3.nabble.com/NPE-from-LHS-of-rule-is-not-returned-by... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users

Your example has openned my eyes to a few facts

rule "policyDefinition.Coverage" agenda-group "policyDefinition" when $p : Policy() $cov : Coverage() from $p.coverageList then try { insert($cov); } catch (Exception e) { e.printStackTrace(); } end