title: symfony boolean field into form
body: <p>I have this field in entity:</p>
  
  <pre><code>/**
  * @ORM\Column(type="boolean")
  */
  protected $done = 0;
  </code></pre>
  
  <p>In database it's <code>tinyint(1)</code>. When I try to add it into a form:</p>
  
  <pre><code>$builder
     -&gt;add('done', 'checkbox')
  </code></pre>
  
  <p>It throws an error:</p>
  
  <pre><code>Unable to transform value for property path "done": Expected a Boolean.
  </code></pre>
  
  <p>Huh? Isn't it boolean?</p>