Changes from UNION to OPTIONAL, corresponding with intepretation by new Virtuoso binary
Merge branch 'develop' of https://github.com/openphacts/OPS_LinkedDataApi into develop
Merge branch 'develop' of https://github.com/openphacts/OPS_LinkedDataApi into 1.3.0
Merge branch '1.3.0' of https://github.com/openphacts/OPS_LinkedDataApi into 1.3.0