* value is undefined.
     *
     * @return The location of the problem, never {@code null}.
     */
    String getLocation();

    /**
     * Gets the exception that caused this problem (if any).
     *
     * @return The exception that caused this problem or {@code null} if not applicable.
     */
    Exception getException();

    /**
     * Gets the message that describes this problem.

        for (Vertex v : children) {
            DfsState state = stateMap.putIfAbsent(v, DfsState.VISITING);
            if (state == null) {
                cycle.addLast(v.label);
                List<String> ret = visitCycle(v.children, stateMap, cycle);
                if (ret != null) {
                    return ret;
                }
                cycle.removeLast();
                stateMap.put(v, DfsState.VISITED);

   *
   * @param element the element to add one occurrence of; may be null only if explicitly allowed by
   *     the implementation
   * @return {@code true} always, since this call is required to modify the multiset, unlike other
   *     {@link Collection} types
   * @throws NullPointerException if {@code element} is null and this implementation does not permit
   *     null elements

        return "[ " + "FROM:("
                + (source == null ? "no source" : (source.md == null ? "no source MD" : source.md.toString())) + ") "
                + "TO:(" + (target == null ? "no target" : (target.md == null ? "no target MD" : target.md.toString()))
                + ") " + "version=" + version + ", scope=" + (scope == null ? "null" : scope.getScope()) + ", depth="
                + depth + "]";
    }

    }

    public static UrlQueue<?> getUrlQueue() {
        return URL_QUEUE_THREAD_LOCAL.get();
    }

    public static void setUrlQueue(final UrlQueue<?> urlQueue) {
        if (urlQueue == null) {
            URL_QUEUE_THREAD_LOCAL.remove();
        } else {
            URL_QUEUE_THREAD_LOCAL.set(urlQueue);
        }
    }

    public static CrawlerContext getCrawlerContext() {

  private @interface GwtTransient {}

  /**
   * Compares strings in natural order except that null comes immediately before a given value. This
   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */

   */
  var idleCallback: Runnable? = null
    get() = this.withLock { field }
    set(value) {
      this.withLock { field = value }
    }

  private var executorServiceOrNull: ExecutorService? = null

  @get:JvmName("executorService")
  val executorService: ExecutorService
    get() =
      this.withLock {
        if (executorServiceOrNull == null) {
          executorServiceOrNull =

                        "email": IsDict(
                            {
                                "title": "Email",
                                "anyOf": [{"type": "string"}, {"type": "null"}],
                            }
                        )
                        | IsDict(
                            # TODO: remove when deprecating Pydantic v1

      Path file = createFile();
      if (initialBytes != null) {
        java.nio.file.Files.write(file, initialBytes);
        return MoreFiles.asByteSink(file, StandardOpenOption.APPEND);
      }
      return MoreFiles.asByteSink(file);
    }

    @Override
    public byte[] getExpected(byte[] bytes) {
      if (initialBytes == null) {
        return checkNotNull(bytes);
      } else {

     * from the runtime environment like {@link System#getProperties()} and environment variables.
     *
     * @param systemProperties The system properties, may be {@code null}.
     * @return This request, never {@code null}.
     */
    MavenExecutionRequest setSystemProperties(Properties systemProperties);

    /**