code: function() {
              var err = null, status = parseInt(res.statusCode, 10);
              if (status > 399) { // Unsuccessful HTTP status? Then pass an error to the callback
                  var match = data.match(/^\{"message": "(.+)"\}/i);
                  err = new error.DiscogsError(status, ((match && match[1]) ? match[1] : null));
              }
              callback(err, data, rateLimit);
          }
docs: Pass the data to the callback and pass an error on unsuccessful HTTP status