If a query is done like this:
then the assumption is that it should return all artifacts with property "foo" defined, regardless of the value of "foo". However, if an artifact has the property defined but no value for the property, this query is failing to return it.
1) add an artifact to s-ramp
2) add a custom property "foo" to the artifact, with no value (this can easily be done via the UI)
3) execute the s-ramp query: /s-ramp[@foo]
4) observe that the artifact is not returned