@Override
    public <S2, E2> Traversal.Admin<S2, E2> addStep(final int index, final Step<?, ?> step) throws IllegalStateException {
        return (Traversal.Admin) this;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/EmptyTraversal.java