@Override
    public boolean hasNext() {
        return !this.traverserSet.isEmpty() || this.hostStep.getPreviousStep().hasNext();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java