@Override
    public void reset() {
        super.reset();
        this.duplicateSet.clear();
        this.barrier = null;
        this.barrierIterator = null;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/DedupGlobalStep.java