title: How to deal with KeyErrors correctly
body: <p>As a newbie to Django I'm still learning the ropes my question below is not to do with syntax directly but the best approach.</p>
  
  <p>How would you handle something like below when no value is passed in the url. I get an error.</p>
  
  <pre><code>  cat_id = self.request.GET.get('cat_id', '')
          return Product.objects.filter(category=cat_id)
  </code></pre>