@Override
        public Traversal<Vertex, Double> get_g_withSackX0X_V_outE_sackXsumX_byXweightX_inV_sack_sum() {
            return g.withSack(0.0d).V().outE().sack(sum).by("weight").inV().sack().sum();
        }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/SackTest.java