@Override
    public IsStep<S> clone() {
        final IsStep<S> clone = (IsStep<S>) super.clone();
        clone.predicate = this.predicate.clone();
        return clone;
    }
@author Daniel Kuppitz (http://gremlin.guru)
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/IsStep.java