[rules-users] odd error when trying to update a fact in working memory

Can anyone tell me what this means? It seems as though the fact is being updated elsewhere and is causing the fact handle to not be found, but I have no idea how to go about figuring that out. Is this even what this error message is trying to tell me? java.lang.NullPointerException org.drools.util.AbstractHashTable$EqualityEquals.hashCodeOf(AbstractHashTable.java:325) org.drools.util.ObjectHashMap.remove(ObjectHashMap.java:96) org.drools.reteoo.FromNode.retractTuple(FromNode.java:110) org.drools.reteoo.CompositeTupleSinkAdapter.createAndPropagateRetractTuple(CompositeTupleSinkAdapter.java:83) org.drools.reteoo.LeftInputAdapterNode.retractObject(LeftInputAdapterNode.java:151) org.drools.reteoo.CompositeObjectSinkAdapter.propagateRetractObject(CompositeObjectSinkAdapter.java:375) org.drools.reteoo.ObjectTypeNode.retractObject(ObjectTypeNode.java:180) org.drools.reteoo.Rete.retractObject(Rete.java:214) org.drools.reteoo.ReteooRuleBase.retractObject(ReteooRuleBase.java:211) org.drools.reteoo.ReteooWorkingMemory.doRetract(ReteooWorkingMemory.java:79) org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1231) org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:96) com.kronos.webta.service.smarttime.rules.Rule_Schedule_Day_0.consequence(Rule_Schedule_Day_0.java:20) com.kronos.webta.service.smarttime.rules.Rule_Schedule_Day_0ConsequenceInvoker.evaluate(Rule_Schedule_Day_0ConsequenceInvoker.java:22)