title: Form field value instead of it's index
body: <p>Here is my FormBuilder:</p>
  
  <pre><code>         // EditUserFormType.php
           $builder
                  -&gt;add('eduStartYear', 'choice', array(
                      'label' =&gt; false,
                      'choices' =&gt; range(date('Y'),1956)
                  ))
                  -&gt;add('eduEndYear', 'choice', array(
                      'label' =&gt; false,
                      'choices' =&gt; range(date('Y'),1957),
                  ))
                  -&gt;add('save', 'submit');
  </code></pre>
  
  <p>And this is from Entity:</p>
  
  <pre><code>    /**
       * @ORM\Column(type="date", nullable=true)
       */
      protected $eduStartYear;
  
      /**
       * @ORM\Column(type="date", nullable=true)
       */
      protected $eduEndYear;
  </code></pre>
  
  <p>This is part of controller:</p>
  
  <pre><code>    $user = $this-&gt;getUser();
      $form = $this-&gt;createForm(new EditUserFormType(), $user);
  
      $form-&gt;handleRequest($request);
      if ($form-&gt;isValid()) {
          $em = $this-&gt;getDoctrine()-&gt;getManager();
          $em-&gt;persist($user);
          $em-&gt;flush();
      }
  </code></pre>
  
  <p>I get this error on save:</p>
  
  <blockquote>
    <p>FatalErrorException in DateType.php line 53:</p>
    
    <p>Error: Call to a member function format() on a non-object</p>
  </blockquote>
  
  <p>After I went through all process with debugger I noticed that the value passed to </p>
  
  <p><code>public function convertToDatabaseValue($value, AbstractPlatform $platform)</code></p>
  
  <p>is actually integer, and this integer is the index of form value (eg 0 = 2015, 1 = 2014 etc.)</p>
  
  <p>How do I get value from form field instead of it's index?</p>