title: Boolean logic doesn't work as I expect in twig
body: <pre><code> {{ dump(extend) }}
  </code></pre>
  
  <p>Result:       </p>
  
  <pre><code>  boolean false
  </code></pre>
  
  <p>And when I want to make this:</p>
  
  <pre><code>{% if extend is true %}
      {% extends 'WelcomePageBundle:Default:welcome_page.html.twig' %}
  {% endif %}
  </code></pre>
  
  <p>It doesn't work. Why?</p>
  
  <p>Error:</p>
  
  <pre><code>The test "false" does not exist in FOSUserBundle:ChangePassword:changePassword.html.twig at line 1
  </code></pre>