title: Symfony 2 form field radio required=false?
body: <p>This is part of my entity class :</p>
  
  <pre><code>/**
   * @var integer
   *
   * @ORM\Column(name="student", type="integer", nullable=true)
   */
  private $student;
  </code></pre>
  
  <p>This part of my form class : </p>
  
  <pre><code> $builder
      -&gt;add('student', 'choice', ['label'=&gt; false,
      'expanded' =&gt; true,
      'choices' =&gt; (Array)new StudentEnum(),
     ])
          ;
  </code></pre>
  
  <p>Ad this is output :</p>
  
  <pre><code>&lt;input id="xxxxx_0" type="radio" value="4" required="required" name="xxxxx[student]"&gt;
  &lt;label class="required" for="xxxxxV_student_0"&gt;Nie&lt;/label&gt;
  </code></pre>
  
  <p>...</p>
  
  <p>My problem is that my input tag should not have attribute "required" becouse I have set nullable=true in entity. </p>