@Override
    public <S> Supplier<S> getSackInitialValue() {
        return this.sideEffects.getSackInitialValue();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/MemoryTraversalSideEffects.java