docs: public synchronized Long convertAcls(List<ACL> acls) {
          if (acls == null)
              return -1L;
          // get the value from the map
          Long ret = aclKeyMap.get(acls);
          // could not find the map
          if (ret != null)
              return ret;
          long val = incrementIndex();
          longKeyMap.put(val, acls);
          aclKeyMap.put(acls, val);
          return val;
      }