docs: function (options, cb, wd, params) {
        // if no cb is given, generate a body with the `desiredCapabilities` object
        if (!cb) {
          // check if we have parameters set up
          if (Object.keys(params).length > 0) {
            return JSON.stringify(params);
          }
          return '';
        }
  
        // invoke the given callback & stringify
        var data = cb.call(wd, params);
        return data === null ? '{}' : JSON.stringify(data);
      }