Symfony2.1 - The option "em" does not exist when using DataTransformer
===

I am using [this][1] cookbook recipe to add a data transformer in Symfon 2.1, but I am getting the following error, `The option "em" does not exist. Known options are: "attr", "block_name",....` 

Is this still a valid way to send the entity manager over to the form type?

    $taskForm = $this->createForm(new TaskType(), $task, array(
        'em' => $this->getDoctrine()->getEntityManager(),
    ));


  [1]: http://symfony.com/doc/master/cookbook/form/data_transformers.html
