visionmedia/superagent — pull request #216 by cristiandouce (2013-05-07 20:11:50+00:00)
Title: Avoid undefined values on query parameters at 'serialize(obj)'

From an object like:
```js
var params = {
hello: 'world',
bye: undefined
}
```

the result should only be `hello=world&bye=undefined` if `bye: 'undefined'`