title: Symfony2 : Validating a date using the Form Validator returns error
body: <p>I've added a element to my form which is of type 'date', this then has a validation rule which specifies that the form element value must be of type date, otherwise return an error. However rather than handling the validation, Symfony returns an Exception. See code below:</p>
  
  <p>UserType.php</p>
  
  <pre><code>$builder-&gt;add('startdate', 'date', array(
                'label' =&gt; 'Start Date', 
                'widget' =&gt; 'single_text', 
                'format' =&gt; 'yyyy-MM-dd')
           );
  </code></pre>
  
  <p>Validation.yml</p>
  
  <pre><code>Acme\StoreBundle\Entity\User:
      properties:
          startdate:
              - Date:
                    message: You must specify a valid release date
  </code></pre>
  
  <p>Then when i type '2001-01-aaa' hoping that Symfony will notice the value is not in the right format and handle the error as specified, instead I get this</p>
  
  <pre><code>Failed to match value '2007-01-aaa' with pattern 'yyyy-MM-dd'
  500 Internal Server Error - InvalidArgumentException 
  </code></pre>
  
  <p>Am I doing something wrong here?</p>
  
  <p>Thanks in advance</p>