gistfile1.php

    /**
     * @Route("/contact", name="_demo_contact")
     * @Template()
     */
    public function contactAction(Request $request)
    {
        $contact = new Contact();
        // Set a default for message inside the data object itself.
        // I expect that if message is missing in the request, this value will be used as the default
        $contact->setMessage("Default message from controller");
        // Create the form with $contact as the initial data. Disable csrf to make the test more straightforward.
        $form = $this->createForm(new ContactType(), $contact, ['csrf_protection'   => false]);
        $form->handleRequest($request);

        if ($form->isValid()) {
            return new Response("Good!", 200);
        } else if ($form->isSubmitted()) {
            // $message always returns a validation error even though I've set it on the underlying data object
            return new Response((string)$form->getErrors(true), 400);
        }

        return array('form' => $form->createView());
    }