return actionClass;
    }

    /**
     * Overrides fillInStackTrace to return null for performance optimization.
     * This prevents stack trace generation for this exception type.
     *
     * @return null to skip stack trace generation
     */
    @Override
    public synchronized Throwable fillInStackTrace() {
        return null;
    }

  private static final class TimeoutFutureException extends TimeoutException {
    private TimeoutFutureException(String message) {
      super(message);
    }

    @Override
    public synchronized Throwable fillInStackTrace() {
      setStackTrace(new StackTraceElement[0]);
      return this; // no stack trace, wouldn't be useful anyway
    }
  }

  @Override
  protected @Nullable String pendingToString() {