Map null values to array
<p>Why isn't <code>null</code> added to my <code>keys</code> array below?</p>

<p><strong>HTML</strong></p>

<pre><code>&lt;input type="radio" data-codekey="1"/&gt;
&lt;input type="radio" data-codekey="null"/&gt;
</code></pre>

<p><strong>JS</strong></p>

<pre><code>$(function(){

  var keys = $step.find('input[type="radio"]').map(function (i, el) {

        return $(el).data('codekey');

  }).get();

console.log(keys); // [1]
//desired result: [1, null]

});
</code></pre>

<p><a href="http://jsfiddle.net/Mewem/" rel="nofollow">http://jsfiddle.net/Mewem/</a></p>
