docs: private final Collection<List<String>> catalogKeys(final Collection<String> keyCollections) {
      final Map<Session, List<String>> catalogMap = new HashMap<Session, List<String>>();
  
      for (String key : keyCollections) {
        Session index = this.sessionLocator.getSessionByKey(key);
        List<String> tmpKeys = catalogMap.get(index);
        if (tmpKeys == null) {
          tmpKeys = new ArrayList<String>(10);
          catalogMap.put(index, tmpKeys);
        }
        tmpKeys.add(key);
      }
  
      Collection<List<String>> catalogKeys = catalogMap.values();
      return catalogKeys;
    }