Symfony3.0 使用“实体类型”下拉列表保存表单时;SQL 错误无法插入空值

使用Symfony 3.0，我有一个表单，其中包含从教义实体生成的下拉列表。当我完成表单并提交时，我可以在分析器中看到下拉值已正确传递，但我收到以下错误：知道会发生什么吗？ 编辑我不想传递空值。窗体正在从实体下拉列表中传入所选值。但是插入数据库似乎没有使用它？

SQLSTATE[23000]: [Microsoft][SQL Server Native Client 11.0][SQL Server]Cannot
insert the value NULL into column 'account_type', table 'CRM.dbo.accounts';
column does not allow nulls. INSERT fails.

表格为：（账户类型.php）

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('accountTypeId', EntityType::class, array(
            'class' => 'AppBundle:AccountType',
            'choice_label' => 'typeName',
            //'label' => 'Account Type',
        ))
        ->add('name')
        ->add('notes', null, array('label' => 'Long Name', 'required' => false))
        ->add('address')
        ->add('city')
        ->add('region')
        ->add('country', CountryType::class)
        ->add('postcode')
        ->add('telephone', null, array('required' => false))
        ->add('website', null, array('required' => false))
        ->add('email', null, array('required' => false))
        ->add('save', SubmitType::class);
}

：（帐户控制者.php）

public function addAction(Request $request)
{
    $account = new Account();
    $form = $this->createForm(AccountType::class, $account);
    $form->handleRequest($request);
    if ($form->isSubmitted() && $form->isValid()) {
        try {
            // create account
            //$account = $form->getData();
            // save data to db
            $em = $this->getDoctrine()->getManager();
            $em->persist($account);
            $em->flush();
            // add flash message and return to profile
            $this->addFlash('success', 'Account: ' . $account->getName() .' created successfully.');
            return $this->redirectToRoute('accounts');
        }
        catch(Exception $e) {
            $this->addFlash('error', $e->getMessage());
            return $this->redirectToRoute('accounts');
        }
    }
    // load form for new account
    return $this->render('accounts/add.html.twig', array(
        'form' => $form->createView()
    ));
}

帐户模型关系：

/**
 * @ORM'ManyToOne(targetEntity="AccountType", inversedBy="accounts")
 * @ORM'JoinColumn(name="account_type", referencedColumnName="id")
 */
private $accountTypeName;

帐户类型模型关系：

/**
 * @ORM'OneToMany(targetEntity="Account", mappedBy="accountTypeName")
 */
private $accounts;