code: protected function normalizeOptions(array $options = [])
      {
          $options = parent::normalizeOptions($options);
          if (isset($options['subLiClassLevel0']) && $options['subLiClassLevel0'] !== null) {
              $options['subLiClassLevel0'] = (string) $options['subLiClassLevel0'];
          } else {
              $options['subLiClassLevel0'] = $this->getSubLiClassLevel0();
          }
  
          return $options;
      }
docs: Normalizes given render options.
  
  @param  array $options [optional] options to normalize
  @return array