}

  private fun splitDomain(domain: String): List<String> {
    val domainLabels = domain.split('.')

    if (domainLabels.last() == "") {
      // allow for domain name trailing dot
      return domainLabels.dropLast(1)
    }

    return domainLabels
  }

  private fun findMatchingRule(domainLabels: List<String>): List<String> {
    if (!listRead.get() && listRead.compareAndSet(false, true)) {

        visit(g.getEntry(), visited, g);

        List<MetadataGraphVertex> dropList = new ArrayList<>(g.getVertices().size());

        // collect drop list
        for (MetadataGraphVertex v : g.getVertices()) {
            if (!visited.contains(v)) {
                dropList.add(v);
            }
        }

        if (dropList.size() < 1) {
            return g;
        }

        // now - drop vertices

* ♻️ Move from `Optional[X]` to `Union[X, None]` for internal utils. PR [#5124](https://github.com/tiangolo/fastapi/pull/5124) by [@tiangolo](https://github.com/tiangolo).
* 🔧 Update sponsors, remove Dropbase, add Doist. PR [#5096](https://github.com/tiangolo/fastapi/pull/5096) by [@tiangolo](https://github.com/tiangolo).