private static <T> void persist(Map<String, T> map, PersistentHashMap<String, T> persistentMap) throws IOException {
    for (Map.Entry<String, T> each : map.entrySet()) {
      persistentMap.put(each.getKey(), each.getValue());
    }
  }
private static <T> void persist(Map<String, T> map, PersistentHashMap<String, T> persistentMap)