* refresh.
     */
    @CanIgnoreReturnValue
    @Nullable V refresh(K key, int hash, CacheLoader<? super K, V> loader, boolean checkTime) {
      LoadingValueReference<K, V> loadingValueReference =
          insertLoadingValueReference(key, hash, checkTime);
      if (loadingValueReference == null) {
        return null;
      }

     * refresh.
     */
    @CanIgnoreReturnValue
    @Nullable V refresh(K key, int hash, CacheLoader<? super K, V> loader, boolean checkTime) {
      LoadingValueReference<K, V> loadingValueReference =
          insertLoadingValueReference(key, hash, checkTime);
      if (loadingValueReference == null) {
        return null;
      }