@Override
    public SackValueStep<S, A, B> clone() {
        final SackValueStep<S, A, B> clone = (SackValueStep<S, A, B>) super.clone();
        if (null != this.sackTraversal)
            clone.sackTraversal = this.sackTraversal.clone();
        return clone;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/SackValueStep.java