title: Map null values to array
body: <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>