code: function decode_param(val) {
    if (typeof val !== 'string' || val.length === 0) {
      return val;
    }
  
    try {
      return decodeURIComponent(val);
    } catch (err) {
      if (err instanceof URIError) {
        err.message = `Failed to decode param '${val}'`;
        err.status = err.statusCode = 400;
      }
  
      throw err;
    }
  }
docs: Decode param value.
  
  @param {string} val
  @return {string}
  @private