code: public synchronized List<GoogleCloudStorageItemInfo> getList(
        String bucket, @Nullable String objectNamePrefix) {
      PrefixKey key = new PrefixKey(bucket, objectNamePrefix);
      Entry<PrefixKey, CacheValue<Object>> entry = getParentEntry(prefixMap, key);
  
      if (entry == null) {
        return null;
      }
  
      if (isExpired(entry.getValue())) {
        cleanupLists(key);
        return null;
      }
  
      return listItems(key);
    }
docs: Gets the cached list associated with the given bucket and object name prefix.
  
  @param bucket the bucket where the entries are being retrieved from.
  @param objectNamePrefix the object name prefix to match against. If this is empty string or
  null, it will match everything in the bucket.
  @return a list of items matching in the given bucket matching the given object name prefix,
  null if a list isn't found or the is expired.