docs: private List<CompletableFuture<Channel>> getChannelPool(Address address) {
      List<CompletableFuture<Channel>> channelPool = channels.get(address);
      if (channelPool != null) {
        return channelPool;
      }
      return channels.computeIfAbsent(address, e -> {
        List<CompletableFuture<Channel>> defaultList = new ArrayList<>(size);
        for (int i = 0; i < size; i++) {
          defaultList.add(null);
        }
        return Lists.newCopyOnWriteArrayList(defaultList);
      });
    }