NullPointerException after stream garbage collection runs in BRMS 6.0.3

Issue

Caused by: java.lang.NullPointerException
at org.drools.core.util.AbstractHashTable$SingleIndex.equal(AbstractHashTable.java:512)
at org.drools.core.util.index.LeftTupleList.matches(LeftTupleList.java:272)
at org.drools.core.util.index.LeftTupleIndexHashTable.getOrCreate(LeftTupleIndexHashTable.java:460)
at org.drools.core.util.index.LeftTupleIndexHashTable.add(LeftTupleIndexHashTable.java:379)
at org.drools.core.phreak.PhreakJoinNode.doLeftInserts(PhreakJoinNode.java:84)
at org.drools.core.phreak.PhreakJoinNode.doNode(PhreakJoinNode.java:60)
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:334)
at org.drools.core.phreak.RuleNetworkEvaluator.outerEval(RuleNetworkEvaluator.java:161)
at org.drools.core.phreak.RuleNetworkEvaluator.evaluateNetwork(RuleNetworkEvaluator.java:116)
at org.drools.core.phreak.RuleExecutor.reEvaluateNetwork(RuleExecutor.java:227)
at org.drools.core.phreak.RuleExecutor.evaluateNetworkAndFire(RuleExecutor.java:98)
at org.drools.core.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:952)
at org.drools.core.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1222)
at org.drools.core.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:950)
at org.drools.core.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:924)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:256)

remove tuples from the right memory when gc'ing them