changed no-op logic on empty values. must be codebooked to conversion:null to be omitted. done to handle use case where an empty string is to be interpreted as a "useful" non-empty string.
changed no-op logic on empty values. must be codebooked to conversion:null to be omitted. done to handle use case where an empty string is to be interpreted as a "useful" non-empty string.

timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation,timrdf/csv2rdf4lod-automation