@Override
    public DateAddStep<S> clone() {
        final DateAddStep<S> clone = (DateAddStep<S>) super.clone();
        clone.value = this.value;
        clone.duration = this.duration;
        clone.dateToken = this.dateToken;
        return clone;
    }
Reference implementation for date concatenation step.

@author Valentyn Kahamlyk
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/DateAddStep.java