以编辑形式上传symfony 3文件

Question

我有一个带有字段“图像”的实体“Cours” 这是CoursType.php的构建器

$builder
        ->add('titre')
        ->add('image', FileType::class, array('data_class' => null, 'label'=>false,'required'=>false))                                                                                       
        ->add('videoIntro')
            );

问题在于“”编辑表单“”，当我提交此表单而不上传新图像时，空值将传递给“图像”。

这是editAction的控制器代码

public function editAction(Request $request, Cours $cour)
{   
    $em = $this->getDoctrine()->getManager();

    $deleteForm = $this->createDeleteForm($cour);


    $editForm = $this->createForm('LearnBundle\Form\CoursType', $cour);
    $editForm->handleRequest($request);

    if ($editForm->isSubmitted() && $editForm->isValid())
    {

        $image=$cour->getImage();
        $imageName = md5(uniqid()).'.'.$image->guessExtension();
        $image->move($this->getParameter('images_directory'),$imageName);
        $cour->setImage($imageName);

        $em->flush();

        return $this->redirectToRoute('cours_edit', array('id' => $cour->getId()));
    }

    return $this->render('cours/edit.html.twig', array(
        'cour' => $cour,
        'edit_form' => $editForm->createView(),
        'delete_form' => $deleteForm->createView(),

    ));
}