setStackTrace(new StackTraceElement[0]);
      return this; // no stack trace, wouldn't be useful anyway
    }
  }

  @Override
  protected @Nullable String pendingToString() {
    @RetainedLocalRef ListenableFuture<? extends V> localInputFuture = delegateRef;
    @RetainedLocalRef ScheduledFuture<?> localTimer = timer;
    if (localInputFuture != null) {