title: How to return 'null' instead of 'undefined' from select element
body: <p>How can I return null instead of a 'undefined' from a select element.</p>
  
  <p>Basically I have 4 selects at the moment, but only the first one is populated with data at this point, but I want to grab the value from all of them when working with them.</p>
  
  <pre><code>&lt;select class="changeValue" id="drpOne"&gt;&lt;/select&gt;
  &lt;option id=1&gt;1&lt;/option&gt;
  &lt;option id=2&gt;2&lt;/option&gt;
  &lt;option id=3&gt;3&lt;/option&gt;
  
  &lt;select class="changeValue" id="drpTwo"&gt;&lt;/select&gt;
  </code></pre>
  
  <p>JQuery:</p>
  
  <pre><code>$('.changeValue').change(function() {
      var data = {};
      data["Id1"] = $('#drpOne:selected').attr("id");
      data["Id2"] = $('#drpTwo:selected').attr("id");
  </code></pre>
  
  <p>In this case, drpTwo will return 'undefined'. Is there anyway to get a null instead?</p>