}

    protected Stream<BuildStep> nonEmptyPredecessors(BuildStep step) {
        HashSet<BuildStep> preds = new HashSet<>();
        nonEmptyPredecessors(step, preds, new HashSet<>());
        return preds.stream();
    }

    private void nonEmptyPredecessors(BuildStep step, Set<BuildStep> preds, Set<BuildStep> visited) {
        if (visited.add(step)) {