@Override
    public TraversalSelectStep<S, E> clone() {
        final TraversalSelectStep<S, E> clone = (TraversalSelectStep<S, E>) super.clone();
        clone.keyTraversal = this.keyTraversal.clone();
        if (null != this.selectTraversal)
            clone.selectTraversal = this.selectTraversal.clone();
        return clone;
    }
@author Daniel Kuppitz (http://gremlin.guru)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/TraversalSelectStep.java