@Override
    public TraversalFlatMapStep<S, E> clone() {
        final TraversalFlatMapStep<S, E> clone = (TraversalFlatMapStep<S, E>) super.clone();
        clone.flatMapTraversal = this.flatMapTraversal.clone();
        return clone;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/TraversalFlatMapStep.java