added test case for default graph
added test case for default graph

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