public static function ensureArrayKeys($key) {
    if (empty($key)) {
      return array();
    }
    if (!is_array($key)) {
      if (strstr($key, '|')) {
        $key = str_replace('|', self::ARRAY_DELIMITER, $key);
      }
      $key = explode(self::ARRAY_DELIMITER, $key);
    }
    return $key;
  }