Potential bug in handling of empty VALUES clauses

[Manuel Fiorelli]

Dear all,

I was updating my own code base to RDF4J 3.7.0, when I discovered what appears to be a bug in the handling of empty CLAUSES sections.

For your convenience, I provide a very simple test case showing the problem.

The following query works as expected (tested on a memory store)

SELECT * {  
  VALUES(?dataset ?urispace) {
    (<http://example.org/void.ttl#ExampleDataset> "http://example.org/")
  }
  FILTER(STRSTARTS(STR(<http://example.org/Person>), ?urispace))
}

It returns the following the solution:

Dataset	Urispace
<http://example.org/void.ttl#ExampleDataset>	"http://example.org/"

In my code bases the VALUES clause is populated programmatically, and it can happen that it is empty, like in the query below:

SELECT * {  
  VALUES(?dataset ?urispace) {
  }
  FILTER(STRSTARTS(STR(<http://example.org/Person>), ?urispace))
}

The query fails with the following log:

java.util.NoSuchElementException: null
at java.util.ArrayList$Itr.next(ArrayList.java:864)
at org.eclipse.rdf4j.query.algebra.evaluation.impl.BindingSetAssignmentInliner$BindingSetAssignmentVisitor.meet(BindingSetAssignmentInliner.java:46)
at org.eclipse.rdf4j.query.algebra.BindingSetAssignment.visit(BindingSetAssignment.java:49)
at org.eclipse.rdf4j.query.algebra.UnaryTupleOperator.visitChildren(UnaryTupleOperator.java:79)
at org.eclipse.rdf4j.query.algebra.Filter.visitChildren(Filter.java:75)
at org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor.meetNode(AbstractQueryModelVisitor.java:572)
at org.eclipse.rdf4j.query.algebra.evaluation.impl.BindingSetAssignmentInliner$BindingSetAssignmentVisitor.meetNode(BindingSetAssignmentInliner.java:82)
at org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor.meetUnaryTupleOperator(AbstractQueryModelVisitor.java:592)
at org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor.meet(AbstractQueryModelVisitor.java:230)
at org.eclipse.rdf4j.query.algebra.evaluation.impl.BindingSetAssignmentInliner$BindingSetAssignmentVisitor.meet(BindingSetAssignmentInliner.java:63)
at org.eclipse.rdf4j.query.algebra.Filter.visit(Filter.java:69)
at org.eclipse.rdf4j.query.algebra.UnaryTupleOperator.visitChildren(UnaryTupleOperator.java:79)
at org.eclipse.rdf4j.query.algebra.Projection.visitChildren(Projection.java:81)
at org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor.meetNode(AbstractQueryModelVisitor.java:572)
at org.eclipse.rdf4j.query.algebra.evaluation.impl.BindingSetAssignmentInliner$BindingSetAssignmentVisitor.meetNode(BindingSetAssignmentInliner.java:82)
at org.eclipse.rdf4j.query.algebra.helpers.AbstractQueryModelVisitor.meetUnaryTupleOperator(AbstractQueryModelVisitor.java:592)
at...

These queries were working on a previous version of RDF4J (3.2.3).

Regards,

Manuel Fiorelli

[Jeen Broekstra]

This is definitely a bug - could you log an issue for it please? It is probably a regression introduced by this improvement: https://github.com/eclipse/rdf4j/issues/3008 . 

Cheers,

Jeen

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[Manuel Fiorelli]

Hi Jeen

thank you for the prompt reply to this email and to the other one I sent yesterday. I filed two separate issues: https://github.com/eclipse/rdf4j/issues/3090 and https://github.com/eclipse/rdf4j/issues/3091

Regards

Manuel

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Manuel Fiorelli