code: protected InputStream openAsset(String path) throws IOException {
      String fullPath = normalizePath(pathPrefix + path);
      InputStream is = (expansionLoader == null) ?
        assetMgr.open(fullPath, AssetManager.ACCESS_STREAMING) :
        expansionLoader.openStream(fullPath);
      if (is == null)
        throw new FileNotFoundException("Missing resource: " + fullPath);
      return is;
    }
docs: Attempts to open the asset with the given name, throwing an {@link IOException} in case of
  failure.