[rules-users] NPE with modify

I am getting an NPE when I uncomment the modify call in the rule below. I am running version 3.0.4. I'd appreciate any ideas as to why this is happening. Thanks, Scott rule "TEST" when $paystub: Paystub( $grossPay: grossPay ) eval( $grossPay.getState() == FPConstants.INACTIVE ) then $grossPay.setState( FPConstants.READY ); //modify( $paystub ); end With modify uncommented I get the following exception: java.lang.NullPointerException at org.drools.reteoo.beta.DefaultRightMemory.remove(Unknown Source) at org.drools.reteoo.BetaMemory.remove(Unknown Source) at org.drools.reteoo.JoinNode.modifyObject(Unknown Source) at org.drools.reteoo.ObjectSource.propagateModifyObject(Unknown Source) at org.drools.reteoo.ObjectTypeNode.modifyObject(Unknown Source) at org.drools.reteoo.Rete.modifyObject(Unknown Source) at org.drools.reteoo.ReteooRuleBase.modifyObject(Unknown Source) at org.drools.reteoo.ReteooWorkingMemory.modifyObject(Unknown Source) at org.drools.base.DefaultKnowledgeHelper.modifyObject(Unknown Source) at org.fp.findata.Rule_Precalc___TEST_0.consequence(Rule_Precalc___TEST_0.java:14) at org.fp.findata.Rule_Precalc___TEST_0ConsequenceInvoker.evaluate(Rule_Precalc___TEST_0ConsequenceInvoker.java:29) at org.drools.common.DefaultAgenda.fireActivation(Unknown Source) at org.drools.common.DefaultAgenda.fireNextItem(Unknown Source) at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown Source) at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown Source) at org.fp.util.RuleEngineManager$RunTask.run(RuleEngineManager.java:159)