BI-17 query variant fails.

[glennga]

The following variant of BI-17 raises a runtime error (somewhere in the probe phase of one PBJ, there is an error):

SET `graphix.semantics.pattern` "homomorphism";

FROM
    GRAPH SNB.Native.SNBGraph
        (person1:Person)<-[:HAS_CREATOR]-(message1:Message),
        (message1)-[:REPLY_OF*]->(post1:Message)<-[:CONTAINER_OF]-(forum1:Forum),
        (message1)-[:HAS_TAG]->(tag:Tag),
        (forum1)-[:HAS_MEMBER]->(person2:Person)<-[:HAS_CREATOR]-(comment:Message)-[:HAS_TAG]->(tag),
        (forum1)-[:HAS_MEMBER]->(person3:Person)<-[:HAS_CREATOR]-(message2:Message),
        (comment)-[:REPLY_OF]->(message2)-[:REPLY_OF*]->(post2:Message)<-[:CONTAINER_OF]-(forum2:Forum)
WHERE
    post1.isPost AND
    post2.isPost AND
    NOT comment.isPost AND
    forum1.id != forum2.id AND
    person2.id != person3.id AND
    tag.name = "Break_Every_Rule" AND
    message2.creationDate > message1.creationDate + DURATION("P" + 12 + "H") AND
    NOT EXISTS (
        FROM
            GRAPH SNB.Native.SNBGraph
                (forum2)-[:HAS_MEMBER]->(person1)
        SELECT
            1
    )
GROUP BY
    person1.id AS person1Id
SELECT
    person1Id                   AS person1Id,
    COUNT(DISTINCT message2.id) AS messageCount
ORDER BY
    messageCount DESC,
    person1Id ASC
LIMIT
    10;

Yields the error below. The message returned to the UI varies from "NPE" to the "request-cancelled".

org.apache.hyracks.api.exceptions.HyracksDataException: java.lang.NullPointerException
        at org.apache.hyracks.api.exceptions.HyracksDataException.create(HyracksDataException.java:70) ~[hyracks-api-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.api.util.ExceptionUtils.setNodeIds(ExceptionUtils.java:70) ~[hyracks-api-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.control.nc.Task.run(Task.java:398) ~[hyracks-control-nc-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[?:?] 
        at java.lang.Thread.run(Thread.java:829) ~[?:?]
Caused by: java.lang.NullPointerException
        at java.util.Objects.requireNonNull(Objects.java:221) ~[?:?]
        at org.apache.asterix.dataflow.data.common.TaggedValueReference.set(TaggedValueReference.java:32) ~[asterix-om-0.9.9-SNAPSHOT.jar:0.9.9-SNAPSHOT]
        at org.apache.asterix.runtime.evaluators.comparisons.AbstractComparisonEvaluator.evaluate(AbstractComparisonEvaluator.java:111) ~[asterix-runtime-0.9.9-SNAPSHOT.jar:0.9.9-SNAPSHOT]
        at org.apache.hyracks.algebricks.runtime.evaluators.TuplePairEvaluatorFactory$TuplePairEvaluator.compare(TuplePairEvaluatorFactory.java:81) ~[algebricks-runtime-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.dataflow.std.join.InMemoryHashJoin.join(InMemoryHashJoin.java:215) ~[hyracks-dataflow-std-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.dataflow.std.join.OptimizedHybridHashJoin.probe(OptimizedHybridHashJoin.java:510) ~[hyracks-dataflow-std-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.dataflow.std.join.OptimizedHybridHashJoinOperatorDescriptor$ProbeAndJoinActivityNode$ProbeAndJoinPushRuntime.applyHybridHashJoin(OptimizedHybridHashJoinOperatorDescriptor.java:690) ~[hyracks-dataflow-std-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.dataflow.std.join.OptimizedHybridHashJoinOperatorDescriptor$ProbeAndJoinActivityNode$ProbeAndJoinPushRuntime.joinPartitionPair(OptimizedHybridHashJoinOperatorDescriptor.java:635) ~[hyracks-dataflow-std-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at org.apache.hyracks.dataflow.std.join.PersistentBuildJoinOperatorDescriptor$TransientProbeActivityNode$1.lambda$nextFrame$0(PersistentBuildJoinOperatorDescriptor.java:291) ~[hyracks-dataflow-std-0.3.9-SNAPSHOT.jar:0.3.9-SNAPSHOT]
        at java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[?:?]
        ... 3 more