fix data/attr return value issue with jQuery prior to version 1.7.2

There is an issue with a return value of `.data()`/`.attr()` which [this plnkr demonstrates](http://plnkr.co/edit/9k9gwW?p=preview): when you pass an `undefined` as a `value` to each of these functions they will return `undefined` instead of the set of elements you call this method upon. This will raise a `TypeError` when trying to chain (effectively calling a method of `undefined`). Also this is the only place in the code where these methods are chained.