code: private File getKeenCacheDirectory() throws IOException {
          File file = new File(root, "keen");
          if (!file.exists()) {
              boolean dirMade = file.mkdir();
              if (!dirMade) {
                  throw new IOException("Could not make keen cache directory at: " + file.getAbsolutePath());
              }
          }
          return file;
      }
docs: Gets the root directory of the Keen cache, based on the root directory passed to the
  constructor of this file store. If necessary, this method will attempt to create the
  directory.
  
  @return The root directory of the cache.