I'm wondering if `!== null` is a good strategy? Is there a guarantee that getAttribute returns null in the undefined case?

From [MDN](https://developer.mozilla.org/en-US/docs/Web/API/element.getAttribute#Notes):
>Essentially all web browsers (Firefox, Internet Explorer, recent versions of Opera, Safari, Konqueror, and iCab, as a non-exhaustive list) return null when the specified attribute does not exist on the specified element and this is what the current DOM specification draft specifies. The old DOM 3 Core specification, on the other hand, says that the correct return value in this case is actually the empty string, and some DOM implementations implement this behavior.

I realize "some DOM implementations" might not involve supported browsers, but just throwing that out there