@Override
    public void addStarts(final Iterator<Traverser.Admin<S>> starts) {
        if (starts.hasNext()) {
            this.done = false;
            super.addStarts(starts);
        }
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/SupplyingBarrierStep.java