Getting empty string instead of undefined from unset attributes using jQuery

The jQuery documentation states that

As of jQuery 1.6, the .attr() method returns undefined for attributes that have not been set.

However, I have a case where I'd like a method to return undefined if I go looking for an attribute that is not defined, but an empty string for attributes that have been set to have no value.

Given the following markup:

<p data-withvalue="hello there!" data-novalue="">

I'd like javascript that works like this:

$('p').attr('data-withvalue') => "hello there!"
$('p').attr('data-noval开发者_开发问答ue') => ""
$('p').attr('data-notthere') => undefined

Downgrading jQuery is not an option. Is this possible?

(Note: looking at "inspect element" in the Chrome developer tools, I note that data-novalue="" has been changed to data-novalue. I don't know if all browsers interpret it like that, but I need this to be cross-browser compatible...)

Unless I'm mistaken, that's exactly how it's working with jQuery 1.6.2

Demo: http://jsfiddle.net/xJfpX/

Output:

hello there!

undefined