mootools/mootools-core — pull request #2403 by gonchuki (2012-08-10 18:15:50+00:00)
Title: do not allow getComputedStyle to return null

#2326 uncovered a bug where an empty element that was never attached to the DOM was returning null on `getComputedStyle('margin-left')` (or any margin).

I tracked this to being that getComputedStyle was returning `null` when it couldn't determine the style, however the browser behavior is that unset styles return an empty string while styles that don't exist act as any key that doesn't exist on an object (returning undefined).