symfony2表单绑定请求返回500错误

所以我有一个表单类型“PictureType”：

当我提交表格时，它给了我500个错误

"The controller must return a response (null given). Did you forget to add a return statement somewhere in your controller?" 

---

有人能帮我吗：（？

不要使用echo，控制器必须返回响应：

    $form->bindRequest($this->get('request')); // this line gives the error

    if( $form->isValid() )
    {
         return new Response('Hello world!');
    }

请参阅以下链接：

use AB\MyBundle\Form\Type\PictureType;
use AB\MyBundle\Form\Model\Picture;
 ...
 ...

$form = $this->createForm(new PictureType, new Picture); 
    if( $this->get('request')->getMethod() == 'POST' )
    {
    echo "1"; // 1 is printed
        $form->bindRequest($this->get('request')); // this line gives the error

        echo "2"; // 2 is not printed
        if( $form->isValid() )
        {

         }
    }

    return $this->render("ABMyBundle:Default:pic.html.twig",array(
            'form' => $form->createview()

    ));

"The controller must return a response (null given). Did you forget to add a return statement somewhere in your controller?" 

    $form->bindRequest($this->get('request')); // this line gives the error

    if( $form->isValid() )
    {
         return new Response('Hello world!');
    }

$form = $this->createForm(new PictureType, new Picture); 
if( $this->get('request')->getMethod() == 'POST' )
{
    echo "1";
    $form->bind($request);         
    if( $form->isValid() )
    {
       echo "2"; 
    }
}