code: function validateBody(err, body) {
        body = tryParse(body);
  
        if (err || !body) {
          return next(err || new Error('Unparsable response with statusCode ' + statusCode));
        }
  
        if (statusCode !== 200) {
          return next(new Error(body.message || 'Invalid status code ' + statusCode));
        }
  
        next(null, body);
      }
docs: If a callback is passed, validate the returned body