@Override
    public Traverser.Admin<S> remove() {  // pop, exception if empty
        final Iterator<Traverser.Admin<S>> iterator = this.map.values().iterator();
        if (!iterator.hasNext())
            throw FastNoSuchElementException.instance();
        final Traverser.Admin<S> next = iterator.next();
        iterator.remove();
        return next;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/traverser/util/TraverserSet.java