@Override
    public Iterator<Vertex> vertices(final Object... vertexIds) {
        return Collections.emptyIterator();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/empty/EmptyGraph.java