docs: @SuppressWarnings("unchecked")
      public CompletableFuture<Void> close() {
  
          this.closed = true;
  
          List<CompletableFuture<Void>> futures = new ArrayList<>();
  
          forEach((connectionKey, closeable) -> {
  
              futures.add(closeable.closeAsync());
              connections.remove(connectionKey);
          });
  
          return Futures.allOf(futures);
      }