I persist a KieSession via the Marshaller (serializable) with one fact/event inserted. On reload of the session, I can see that fact is still there (when I check the FactHandles) and the PseudoClock is at the correct time (the time when I persisted it). If I then insert another fact/event into this reloaded session which matches the following rule:

rule "SimpleFactTimeWindow"
when
$s1: SimpleFact() from entry-point LinkyStream
$s2: SimpleFact(this != $s1, this after [0s, 10s] $s1) from entry-point LinkyStream
then
System.out.println("Rule fired, found 2 Facts within the time window.");
end

I get a NPE (in both Phreak and ReteOO mode). Exception in Phreak:
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:297)
at java.lang.Thread.run(Thread.java:724)
Caused by: java.lang.NullPointerException
at org.drools.core.base.evaluators.AfterEvaluatorDefinition$AfterEvaluator.evaluateCachedRight(AfterEvaluatorDefinition.java:304)
at org.drools.core.rule.constraint.EvaluatorConstraint.isAllowedCachedRight(EvaluatorConstraint.java:80)
at org.drools.core.common.DoubleBetaConstraints.isAllowedCachedRight(DoubleBetaConstraints.java:117)
at org.drools.core.phreak.PhreakJoinNode.doRightInserts(PhreakJoinNode.java:150)
at org.drools.core.phreak.PhreakJoinNode.doNode(PhreakJoinNode.java:56)
at org.drools.core.phreak.RuleNetworkEvaluator.switchOnDoBetaNode(RuleNetworkEvaluator.java:547)
at org.drools.core.phreak.RuleNetworkEvaluator.evalBetaNode(RuleNetworkEvaluator.java:533)
at org.drools.core.phreak.RuleNetworkEvaluator.innerEval(RuleNetworkEvaluator.java:335)
at org.drools.core.phreak.RuleNetworkEvaluator.outerEval(RuleNetworkEvaluator.java:162)
at org.drools.core.phreak.RuleNetworkEvaluator.evaluateNetwork(RuleNetworkEvaluator.java:117)
at org.drools.core.phreak.RuleExecutor.reEvaluateNetwork(RuleExecutor.java:194)
at org.drools.core.phreak.RuleExecutor.evaluateNetworkAndFire(RuleExecutor.java:65)
at org.drools.core.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:936)
at org.drools.core.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1183)
at org.drools.core.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:936)
at org.drools.core.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:910)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:233)
at org.jboss.ddoyle.brms.cep.ha.management.TestScenarioRunner.secondRun(TestScenarioRunner.java:142)
at org.jboss.ddoyle.brms.cep.ha.management.MainSecondRun.main(MainSecondRun.java:7)
... 6 more

Exception in ReteOO:
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:297)
at java.lang.Thread.run(Thread.java:724)
Caused by: org.drools.core.RuntimeDroolsException: Unexpected exception executing action org.drools.core.reteoo.PropagationQueuingNode$PropagateAction@2e3aeda
at org.drools.core.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1225)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:371)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:278)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:131)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:56)
at org.jboss.ddoyle.brms.cep.ha.management.TestScenarioRunner.secondRun(TestScenarioRunner.java:140)
at org.jboss.ddoyle.brms.cep.ha.management.MainSecondRun.main(MainSecondRun.java:7)
... 6 more
Caused by: java.lang.NullPointerException
at org.drools.core.base.evaluators.AfterEvaluatorDefinition$AfterEvaluator.evaluateCachedLeft(AfterEvaluatorDefinition.java:324)
at org.drools.core.rule.constraint.EvaluatorConstraint.isAllowedCachedLeft(EvaluatorConstraint.java:67)
at org.drools.core.common.DoubleBetaConstraints.isAllowedCachedLeft(DoubleBetaConstraints.java:108)
at org.drools.reteoo.nodes.ReteJoinNode.propagateFromLeft(ReteJoinNode.java:147)
at org.drools.reteoo.nodes.ReteJoinNode.assertLeftTuple(ReteJoinNode.java:99)
at org.drools.core.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:213)
at org.drools.core.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:73)
at org.drools.reteoo.nodes.ReteJoinNode.propagateFromRight(ReteJoinNode.java:135)
at org.drools.reteoo.nodes.ReteJoinNode.assertRightTuple(ReteJoinNode.java:125)
at org.drools.reteoo.nodes.ReteBetaNodeUtils.assertObject(ReteBetaNodeUtils.java:47)
at org.drools.reteoo.nodes.ReteJoinNode.assertObject(ReteJoinNode.java:39)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:502)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:387)
at org.drools.core.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:430)
at org.drools.core.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:266)
at org.drools.core.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:592)
at org.drools.core.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1223)
... 12 more

What I discovered is that this only happens when I save the KieSession to a file in one JVM and reload it in another. When I load the KieSession in the same JVM as the one in which I persisted it, there is no exception and the rule get's fired (as expected).

I created a reproducer project for it: https://github.com/DuncanDoyle/DroolsSessionPersistenceNPE/

I've added some Maven profiles so you can easily observe the behaviour:

• mvn -PallRuns exec:java : this runs both the persistence and the reload in the same JVM, no exception, everything works fine.
• mvn -PfirstRun exec:java : this runs the first part of the test, and saves the KieSession to a file.
• mvn -PsecondRun exec:java : this runs the second part of the test, which loads the previously saved KieSession from the file and inserts a new fact, resulting in the NPE.

All three tests can also be run in ReteOO mode by adding "-Ddrools.ruleEngine=reteoo" at the end of the command.