title: How can I test a template tag {% url %} in the shell?
body: <p>I have a project in production. Everthing was working fun, but suddenly, I'm getting an error:  </p>
  
  <pre><code>Caught NoReverseMatch while rendering: Reverse for 'forum.views.tag' with arguments '(u'',)' and keyword arguments '{}' not found. 
  </code></pre>
  
  <p>I believe this is being called by this line from the template:</p>
  
  <pre><code>href="{% url forum.views.tag tag|urlencode %}"
  </code></pre>
  
  <p>from urls.py:  </p>
  
  <pre><code>(r'^tags/$', app.tags),  
  (r'^tags/(?P&lt;tag&gt;[^/]+)/$', app.tag),
  </code></pre>
  
  <p>How can I simulate this call from the shell?<br>
  What could be causing this error?</p>