Better exceptions raised for illegal triple combinations
Better exceptions raised for illegal triple combinations

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