Daniel Kuppitz created TINKERPOP-2095:
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             Summary: GroupStep looks for irrelevant barrier steps
                 Key: TINKERPOP-2095
                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2095
             Project: TinkerPop
          Issue Type: Bug
          Components: process
    Affects Versions: 3.3.4
            Reporter: Daniel Kuppitz
            Assignee: Daniel Kuppitz


{{GroupStep}} looks for {{Barrier}} step to determine the reducing bi-operator. 
This is wrong and I'm really surprised that this has never been spotted before.

{noformat}
gremlin> 
g.V().hasLabel('person').as('p').out('created').group().by('name').by(select('p').values('age').sum())
java.lang.Long cannot be cast to 
org.apache.tinkerpop.gremlin.process.traversal.traverser.util.TraverserSet
Type ':help' or ':h' for help.
Display stack trace? [yN]
{noformat}

In the query above the first barrier step is a {{NoOpBarrier}} step (added by 
{{PathRetractionStrategy}}). This step obviously has no reducing bi-operator. 
What we really want to do is look for the first reducing barrier step.



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