Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "rdflib/Graph.py", line 679, in query
    return plugin.get('SPARQLQueryResult',QueryResult)(p.query(strOrQuery, initBindings, initNs, DEBUG))
  File "rdflib/sparql/bison/Processor.py", line 39, in query
    return TopEvaluate(strOrQuery,self.graph,initBindings,DEBUG=DEBUG)
  File "rdflib/sparql/Algebra.py", line 239, in TopEvaluate
    result = expr.evaluate(tripleStore,passedBindings,query.prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 518, in evaluate
    self.left = self.left.evaluate(tripleStore,initialBindings,prolog)
  File "rdflib/sparql/Algebra.py", line 533, in evaluate
    _ExpandLeftJoin(self.left.top,self.right,tripleStore,prolog)
  File "rdflib/sparql/Algebra.py", line 498, in _ExpandLeftJoin
    _ExpandLeftJoin(c,expression,tripleStore,prolog)
  File "rdflib/sparql/Algebra.py", line 498, in _ExpandLeftJoin
    _ExpandLeftJoin(c,expression,tripleStore,prolog)
  File "rdflib/sparql/Algebra.py", line 498, in _ExpandLeftJoin
    _ExpandLeftJoin(c,expression,tripleStore,prolog)
  File "rdflib/sparql/Algebra.py", line 498, in _ExpandLeftJoin
    _ExpandLeftJoin(c,expression,tripleStore,prolog)
  File "rdflib/sparql/Algebra.py", line 490, in _ExpandLeftJoin
    assert len(list(_fetchBoundLeaves(optTree))) == 1,optTree
AssertionError: <SPARQLNode 140789484. 2 children, 0 OPTs.  clash: False. bound: [u'?label', u'?type', u'?uri', u'?createdate', u'?classlabel']>