title: How to "unset" Dojo datetextbox default?
body: <p>I have a JS overlay layer which sets up data entry controls on my web app as dojo widgets.  I grab inputs like &lt;input type="text" class="date" /&gt; and turn them into <code>DateTextBox</code> widgets.</p>
  
  <p>Here is my basic code:</p>
  
  <pre><code>            var df = dateformat;
              df.replace('mm', 'MM');
              var val = input.value;
              if (val == undefined){
                 val = '';
              }
              return new datebox({
                  "label": input.title,
                  "value": val,
                   "name": input.name,
                     "id": input.id,
            "constraints": { "datePattern": df }
              });
  </code></pre>
  
  <p>My problem is that all DateTextBox's end up set with '1970-00-01' as the initial date if no value is provided.  I would like them to be set to null or undef if no value is provided but this doesn't seem possible until after startup.</p>
  
  <p>Is there a way to set this before I call <code>widget.startup()</code>?</p>