docs: private CompletableFuture<T> orderedFuture() {
      if (!complete) {
        synchronized (orderedFutures) {
          if (!complete) {
            CompletableFuture<T> future = new CompletableFuture<>();
            orderedFutures.add(future);
            return future;
          }
        }
      }
  
      // Completed
      if (error == null) {
        return CompletableFuture.completedFuture(result);
      } else {
        return Futures.exceptionalFuture(error);
      }
    }