return null;
        }
        return header.previous;
    }

    /**
     * Removes the first element.
     *
     * @return the first element
     */
    public E removeFirst() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }
        final E first = header.next.element;
        header.next.remove();
        return first;
    }

    /**

    return poll();
  }

  /**
   * Removes and returns the least element of this queue.
   *
   * @throws NoSuchElementException if the queue is empty
   */
  @CanIgnoreReturnValue
  public E removeFirst() {
    return remove();
  }

  /**
   * Retrieves, but does not remove, the least element of this queue, or returns {@code null} if the
   * queue is empty.
   */
  public @Nullable E peekFirst() {

    return poll();
  }

  /**
   * Removes and returns the least element of this queue.
   *
   * @throws NoSuchElementException if the queue is empty
   */
  @CanIgnoreReturnValue
  public E removeFirst() {
    return remove();
  }

  /**
   * Retrieves, but does not remove, the least element of this queue, or returns {@code null} if the
   * queue is empty.
   */
  public @Nullable E peekFirst() {

        }

        @Override
        public ModelInterpolationException run() {
            while (!interpolationTargets.isEmpty()) {
                Object obj = interpolationTargets.removeFirst();

                try {
                    traverseObjectWithParents(obj.getClass(), obj);
                } catch (ModelInterpolationException e) {
                    return e;
                }

        }

        @Override
        void onEndHtmlElement(String name) {
            if (!tagStack.isEmpty() && tagStack.getFirst().equals(name)) {
                tagStack.removeFirst();
                handlerStack.removeFirst().onEndElement(name);
            }
        }

        @Override
        void onStartJavadocTag(String name) {
            tagValue = new StringBuilder();
        }

             */
            requireNonNull(element);
            if (visited.add(element)) {
              return element;
            }
          }
          horizon.removeFirst();
          return null;
        }
      };
    }

    static <N> Traversal<N> inTree(SuccessorsFunction<N> tree) {
      return new Traversal<N>(tree) {
        @Override

    val pooled1 = planReusePooledConnection()
    if (pooled1 != null) return pooled1

    // Attempt a deferred plan before new routes.
    if (deferredPlans.isNotEmpty()) return deferredPlans.removeFirst()

    // Do blocking calls to plan a route for a new connection.
    val connect = planConnect()

    // Now that we have a set of IP addresses, make another attempt at getting a connection from

        } finally {
          if (doReadTimeout) {
            readTimeout.exitAndThrowIfTimedOut()
          }
        }
      }
      if (headersQueue.isNotEmpty()) {
        return headersQueue.removeFirst()
      }
      throw errorException ?: StreamResetException(errorCode!!)
    }
  }

  /**
   * Returns the trailers if they're immediately available.
   */
  @Throws(IOException::class)

        // Add to history for percentile calculation
        responseTimeHistory.addLast(responseTimeMs);
        if (responseTimeHistory.size() > 1000) { // Keep last 1000 measurements
            responseTimeHistory.removeFirst();
        }

        // Calculate moving average (simple approach)
        if (!responseTimeHistory.isEmpty()) {
            long sum = responseTimeHistory.stream().mapToLong(Long::longValue).sum();