return super.isEmpty();
  }

  /*
   * We don't assert that the lock is held during calls to iterator(), stream(), and spliterator:
   * `Synchronized` doesn't guarantee that it will hold the mutex for those calls because callers
   * are responsible for taking the mutex themselves:
   * https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/util/Collections.html#synchronizedCollection(java.util.Collection)
   *

   * the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
   * documentation.
   */
  public void add(Runnable runnable, Executor executor) {
    // Fail fast on a null. We throw NPE here because the contract of Executor states that it throws
    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");

        case -2:
          // requireNonNull is safe because right must exist in order to get a negative factor.
          requireNonNull(right);
          if (right.balanceFactor() > 0) {
            right = right.rotateRight();
          }
          return rotateLeft();
        case 2:
          // requireNonNull is safe because left must exist in order to get a positive factor.
          requireNonNull(left);

 * set would be sufficient to expose any possible bug. Brute force is simpler.
 *
 * <p>To use this class the concrete subclass must implement the {@link
 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
 * without changing its state, so the tester needs a steady supply of fresh Iterators.
 *
 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the

   *
   * <p>The returned array has all its elements set to their initial null values. However, we don't
   * declare it as {@code @Nullable ImmutableMapEntry[]} because our checker doesn't require newly
   * created arrays to have a {@code @Nullable} element type even when they're created directly with
   * {@code new ImmutableMapEntry[...]}, so it seems silly to insist on that only here.
   */

   * proxy server can issue an auth challenge and then close the connection.
   *
   * @return the next plan to attempt, or null if no further attempt should be made either because
   *     we've successfully connected or because no further attempts should be made.
   */
  @Throws(IOException::class)
  internal fun connectTunnel(): ConnectResult {
    val nextTunnelRequest =
      createTunnel()

      if (node.previousSibling == null) {
        // requireNonNull is safe because we checked that not *both* siblings were null.
        keyList.head = requireNonNull(node.nextSibling);
      } else {
        node.previousSibling.nextSibling = node.nextSibling;
      }

      if (node.nextSibling == null) {
        // requireNonNull is safe because we checked that not *both* siblings were null.

         * don't _want_ our new TypeVariable to be equal to the JDK TypeVariable because it has
         * _different bounds_ than the JDK TypeVariable. And it wouldn't make sense for our new
         * TypeVariable to be equal to any _other_ JDK TypeVariable, either, because any other JDK
         * TypeVariable must have a different declaration or name. The only TypeVariable that our

      return;
    }

    /*
     * Any of the setException() calls below can fail if the output Future is cancelled between now
     * and then. This means that we're silently swallowing an exception -- maybe even an Error. But
     * this is no worse than what FutureTask does in that situation. Additionally, because the

        // this configuration is on fess_env.properties because this is true only when development
        direction.directDevelopmentHere(fessConfig.isDevelopmentHere());

        // titles of the application for logging are from configurations
        direction.directLoggingTitle(fessConfig.getDomainTitle(), fessConfig.getEnvironmentTitle());

        // this configuration is on sea_env.properties because it has no influence to production