@Override
    protected Traverser.Admin<S> processNextStart() throws NoSuchElementException {
        return this.starts.next();
    }
Returns {@code Optional.empty()} if traversal is not iterated or if not locked after strategy application.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ProfileStep.java