title: Check if a variable is defined AND truthy at once in Twig
body: <p>In PHP I can do</p>
  
  <pre><code>&lt;?php if ($someVar): ?&gt;
  </code></pre>
  
  <p>This checks if a variable exists <em>and</em> if its value is different from a zero-like value like 0, null, '', and so on.</p>
  
  <p>Is there any way to do so in Twig or do I need to write my own filter for that? At the moment, I must do</p>
  
  <pre><code>{% if someVar is defined and someVar %}
  </code></pre>
  
  <p>which is a pain when it comes to more complex templates.</p>