Always return a value in CALL subqueries when saving resources

I am not sure whether we actually have a problem here since it previously worked in testing, but according to the neo4j cypher documentation (see here and here), not returning a value in a subquery stops execution of the outer query, which we do not want. This MR makes sure that we always return at least a single value from a subquery. The problem only became apparent while working on the rosetta stone statement branch.