def lookup_vertex(self, index_name, key, value):
        # NOTE: this is different than Rexster's version
        # it uses vertex_path instead of index_path, and 
        # index_name is N/A
        # Keeping method interface the same for practical reasons so
        # index_name will be ignored, any value will work.
        path = build_path(vertex_path)
        params = dict(key=key,value=value)
        return self.request.get(path,params)
Check that the references (self.ref) exists within the build-chain. And, if so,
dataset/ETHPy150Open espeed/bulbs/bulbs/titan/client.py/TitanClient.lookup_vertex--crossover with--dataset/ETHPy150Open appnexus/schema-tool/schematool/command/resolve.py/ResolveCommand._ref_exists