code: private void ensureExists(AlluxioURI path) throws IOException {
      try {
        mFileSystem.getStatus(path);
      } catch (AlluxioException e) {
        throw new IOException(e);
      }
    }
docs: Convenience method which ensures the given path exists, wrapping any {@link AlluxioException}
  in {@link IOException}.
  
  @param path the path to look up