docs: public boolean register(Long streamId, Disposable disposable) {
      boolean result = false;
      if (!disposable.isDisposed()) {
        result = subscriptions.putIfAbsent(streamId, disposable) == null;
      }
      if (result) {
        LOGGER.debug("Registered subscription with sid={}, session={}", streamId, id);
      }
      return result;
    }