In customer's performance test case, NPE happens in TupleSetsImpl.setNextTuple() with the following stack.

java.lang.NullPointerException
at org.drools.core.common.TupleSetsImpl.setNextTuple(TupleSetsImpl.java:352)
at org.drools.core.common.TupleSetsImpl.removeInsert(TupleSetsImpl.java:168)
at org.drools.core.phreak.RuleNetworkEvaluator.deleteChildLeftTuple(RuleNetworkEvaluator.java:729)
at org.drools.core.phreak.RuleNetworkEvaluator.unlinkAndDeleteChildLeftTuple(RuleNetworkEvaluator.java:721)
at org.drools.core.phreak.PhreakNotNode.doRightUpdates(PhreakNotNode.java:343)
at org.drools.core.phreak.PhreakNotNode.doNode(PhreakNotNode.java:74)
at org.drools.core.phreak.RuleNetworkEvaluator.switchOnDoBetaNode(RuleNetworkEvaluator.java:524)
at org.drools.core.phreak.RuleNetworkEvaluator.evalBetaNode(RuleNetworkEvaluator.java:505)
at org.drools.core.phreak.RuleNetworkEvaluator.evalNode(RuleNetworkEvaluator.java:341)
at org.drools.core.phreak.RuleNetworkEvaluator.innerEval(RuleNetworkEvaluator.java:301)
at org.drools.core.phreak.RuleNetworkEvaluator.outerEval(RuleNetworkEvaluator.java:136)
at org.drools.core.phreak.AddRemoveRule.forceFlushLeftTuple(AddRemoveRule.java:692)
at org.drools.core.phreak.AddRemoveRule.flushLeftTupleIfNecessary(AddRemoveRule.java:629)
at org.drools.core.reteoo.NotNode.assertObject(NotNode.java:161)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:494)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:384)
at org.drools.core.reteoo.AlphaNode.assertObject(AlphaNode.java:134)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:494)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:384)
at org.drools.core.reteoo.ObjectTypeNode.propagateAssert(ObjectTypeNode.java:304)
at org.drools.core.phreak.PropagationEntry$Insert.execute(PropagationEntry.java:132)
at org.drools.core.phreak.SynchronizedPropagationList.flush(SynchronizedPropagationList.java:82)
at org.drools.core.phreak.SynchronizedPropagationList.flush(SynchronizedPropagationList.java:72)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.flushPropagations(StatefulKnowledgeSessionImpl.java:2053)
at org.drools.core.phreak.RuleExecutor.fire(RuleExecutor.java:128)
at org.drools.core.phreak.RuleExecutor.evaluateNetworkAndFire(RuleExecutor.java:74)
at org.drools.core.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:960)
at org.drools.core.common.DefaultAgenda.fireLoop(DefaultAgenda.java:1303)
at org.drools.core.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1241)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.internalFireAllRules(StatefulKnowledgeSessionImpl.java:1336)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1327)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1308)