运行balloons.io app时出错？

Question

当我运行balloons.js（https://github.com/gravityonmars/Balloons.IO）时，它会显示以下错误：

url.js:118
throw new TypeError("Parameter 'url' must be a string, not " + typeof url)
      ^
TypeError: Parameter 'url' must be a string, not undefined
at Url.parse (url.js:118:11)
at Object.urlParse [as parse] (url.js:112:5)
at Config (/home/user/Balloons.IO/config/index.js:56:25)
at Object.<anonymous> (/home/user/Balloons.IO/balloons.js:18:20)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)

以上应用使用Redis。