* will not be returned. If existing responses are evicted during iteration, they will be absent
   * (unless they were already returned).
   *
   * The iterator supports [MutableIterator.remove]. Removing a URL from the iterator evicts the
   * corresponding response from the cache. Use this to evict selected responses.
   */
  @Throws(IOException::class)
  fun urls(): MutableIterator<String> {
    return object : MutableIterator<String> {