title: Default datetime data in Silex/Symfony2 forms
body: <p>I'm trying to create a form that will allow users to edit data. I need to read a value from the a table and pre-populate the form with that data. </p>
  
  <p>In the code below I'm trying to set a value of <code>2007-02-20 16:48:00</code> in the form.</p>
  
  <p>What I tried:</p>
  
  <pre><code>$form = $app['form.factory']-&gt;createBuilder( 'form' )
      -&gt;add('start', 'datetime', array(
        'data' =&gt; '2007-02-20 16:48:00')
    )
      -&gt;add('end', 'datetime')
      -&gt;getForm();
  </code></pre>
  
  <p>What I got:</p>
  
  <blockquote>
    <p>UnexpectedTypeException: Expected argument of type "\DateTime",
    "string" given</p>
  </blockquote>
  
  <p>Thanks</p>