Hello, I think I am getting the same/similar problem as described in JBRULES-2796. I am using Drools 5.1.1 with Expert and Flow, here is the stack trace: Caused by: java.lang.NullPointerException at org.drools.reteoo.FromNode.destroyCreatedHandles(FromNode.java:336) at org.drools.reteoo.FromNode.retractLeftTuple(FromNode.java:326) at org .drools .reteoo .CompositeLeftTupleSinkAdapter .doPropagateRetractLeftTuple(CompositeLeftTupleSinkAdapter.java:238) at org .drools .reteoo .CompositeLeftTupleSinkAdapter .propagateRetractRightTuple(CompositeLeftTupleSinkAdapter.java:155) at org.drools.reteoo.JoinNode.retractRightTuple(JoinNode.java:151) at org.drools.reteoo.ObjectTypeNode.retractObject(ObjectTypeNode.java: 232) at org.drools.reteoo.EntryPointNode.retractObject(EntryPointNode.java: 231) at org .drools .common.AbstractWorkingMemory.retract(AbstractWorkingMemory.java:1288) at org .drools .base.DefaultKnowledgeHelper.retract(DefaultKnowledgeHelper.java:201) at org .drools .base.DefaultKnowledgeHelper.retract(DefaultKnowledgeHelper.java:214) at procs .Rule_my_business_rule_0 .defaultConsequence(Rule_my_business_rule_0.java:8) at procs .Rule_my_business_rule_0DefaultConsequenceInvoker .evaluate(Rule_my_business_rule_0DefaultConsequenceInvoker.java:29) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java: 917) The stack trace is different to the one in JBRULES-2796 in that mine is caused by a retract rather than an update. We've created several Flows and associated rules and this issue has only just come up with a recently created one. Firstly, is this the same issue? If it is, where could I find previous releases of Drools so that I may try to downgrade? Alternatively is there some 5.1 -> 5.2 migration documentation? I have tried rewriting the rule that triggers this as there was a comment on rules-dev that this made the error go away though I am having trouble coming up with different ways to write it as it is quite a simple rule. Is there something specific I should try to avoid? -- Gareth Evans Application Developer Geneoz Pty Ltd http://www.geneoz.com gevans(a)geneoz.com +61 8 9212 2200 (Phone) +61 8 9212 2299 (Fax) PO Box 1128 Bentley DC, WA 6983 AUSTRALIA Now Introducing... geneoz VMS The Vivarium Management Solution http://www.geneoz.com ________________________________________________________________ This email contains information that is private and confidential and must be read only by the person to whom it is addressed. This email is not a contract and does not give rise to a legally binding agreement. Prices quoted are valid for 30 days and are subject to exchange rate fluctuations. ________________________________________________________________