@Override
    public <E2> Traversal.Admin<S, E2> addStep(final Step<?, E2> step) {
        return instance();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/EmptyTraversal.java