I just found out thanks to node.js > 0.8 but < 0.10.6, we need this conditional to be:
```js
if (req._decoder || (req._readableState && (req._readableState.encoding !== null || req._readableState.decoder))) {
```
otherwise people using older versions of 0.10 will always trigger this error (since `req._readableState.encoding` will be `undefined`).