This error was first discovered in a proprietary application that is running in wildfly 8.2.1. Up until now I was unable to reproduce outside of the mentioned environment. After narrowing down the exact conditions that cause the error to occur I was able to create a sample project that forces the issue to occur. Below is the stack trace:

Caused by: java.lang.NullPointerException
at org.drools.core.reteoo.BetaMemory.linkNode(BetaMemory.java:93)
at org.drools.core.reteoo.BetaMemory.linkNode(BetaMemory.java:88)
at org.drools.core.reteoo.SingleObjectSinkAdapter.staticDoLinkRiaNode(SingleObjectSinkAdapter.java:111)
at org.drools.core.reteoo.SingleObjectSinkAdapter.doLinkRiaNode(SingleObjectSinkAdapter.java:93)
at org.drools.core.reteoo.RiaPathMemory.doLinkRule(RiaPathMemory.java:52)
at org.drools.core.reteoo.PathMemory.linkSegment(PathMemory.java:103)
at org.drools.core.reteoo.SegmentMemory.notifyRuleLinkSegment(SegmentMemory.java:192)
at org.drools.core.phreak.AddRemoveRule.addNewPaths(AddRemoveRule.java:452)
at org.drools.core.phreak.AddRemoveRule.addRule(AddRemoveRule.java:123)
at org.drools.core.reteoo.builder.ReteooRuleBuilder.addSubRule(ReteooRuleBuilder.java:189)
at org.drools.core.reteoo.builder.ReteooRuleBuilder.addRule(ReteooRuleBuilder.java:133)
at org.drools.core.reteoo.ReteooBuilder.addRule(ReteooBuilder.java:110)
at org.drools.core.impl.KnowledgeBaseImpl.internalAddRule(KnowledgeBaseImpl.java:1530)
at org.drools.core.impl.KnowledgeBaseImpl.lambda$addRules$4(KnowledgeBaseImpl.java:1523)
at org.drools.core.impl.KnowledgeBaseImpl.enqueueModification(KnowledgeBaseImpl.java:734)
at org.drools.core.impl.KnowledgeBaseImpl.addRules(KnowledgeBaseImpl.java:1521)
at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.compileRete(KnowledgeBuilderImpl.java:1010)
at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.buildRules(KnowledgeBuilderImpl.java:2524)
at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.buildPackages(KnowledgeBuilderImpl.java:2450)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.buildPackages(CompositeKnowledgeBuilderImpl.java:109)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.build(CompositeKnowledgeBuilderImpl.java:99)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.rebuildAll(KieContainerImpl.java:473)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.updateKBase(KieContainerImpl.java:309)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.lambda$update$0(KieContainerImpl.java:260)
at org.drools.core.impl.KnowledgeBaseImpl.enqueueModification(KnowledgeBaseImpl.java:734)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.update(KieContainerImpl.java:260)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.updateToVersion(KieContainerImpl.java:199)
at org.drools.test.KieRuntimeManager.buildOnKfs(KieRuntimeManager.java:202)
at org.drools.test.KieRuntimeManager.loadRule(KieRuntimeManager.java:147)
at org.drools.test.DroolsReasonerContainer.loadRule(DroolsReasonerContainer.java:22)
at org.drools.test.App.main(App.java:22)
... 6 more