added asserts for graph.set([s,p,o]) so s and p aren't None
added asserts for graph.set([s,p,o]) so s and p aren't None

otherwise this will delete (*, p, *) or (s, *, *) or even (*, *, *) from graph
and fails on add which is most likely not what the developer wants.

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