fixed datatypes to be a URIRef or None
fixed datatypes to be a URIRef or None

dbs/rdflib,avorio/rdflib,dbs/rdflib,RDFLib/rdflib,armandobs14/rdflib,avorio/rdflib,RDFLib/rdflib,armandobs14/rdflib,marma/rdflib,ssssam/rdflib,yingerj/rdflib,armandobs14/rdflib,dbs/rdflib,RDFLib/rdflib,avorio/rdflib,marma/rdflib,marma/rdflib,dbs/rdflib,yingerj/rdflib,avorio/rdflib,ssssam/rdflib,armandobs14/rdflib,yingerj/rdflib,marma/rdflib,yingerj/rdflib,ssssam/rdflib,ssssam/rdflib,RDFLib/rdflib