@Override
    public CombineStep<S, E> clone() {
        final CombineStep<S, E> clone = (CombineStep<S, E>) super.clone();
        if (null != this.valueTraversal) {
            clone.valueTraversal = this.valueTraversal.clone();
        } else {
            clone.parameterItems = this.parameterItems;
        }
        return clone;
    }
A map step that returns the combination of the traverser and the provided arguments. This is also commonly known as
concatenation or append.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CombineStep.java