title: Exception handling inside twig template
body: <p>i am new to symfony2. my project has two entity</p>
  
  <pre><code>    [1] Category and
      [2] Evaluation
  </code></pre>
  
  <p>and category has many evaluation, so the problem is when i delete the category and then display the evaluation then it display me error like</p>
  
  <p><code>"An exception has been thrown during the rendering of a template ("Entity was not found.") in HfAppBundle:SpecificEvaluations:index.html.twig at line 137. "</code>.</p>
  
  <p>on line number 137 this is the content <code>{{evaluation.category.name}}</code>. i had also try with </p>
  
  <pre><code>    {% if evaluation.category.name is not null %}
          {{evaluation.category.name}}
      {% endif %}
  </code></pre>
  
  <p>but it also give me same error.
  any one can help ?</p>
  
  <p>thanks</p>