title: django 1.6 url tag error
body: <p>I have problem with my app1 application :</p>
  
  <pre><code>Reverse for 'app1.views.add_content' with arguments '('',)' and keyword arguments '{}' not found. 1 pattern(s) tried: ['/add-content/(\\d+)/$']
  </code></pre>
  
  <p>views</p>
  
  <pre><code>@login_required
  def add_content(request, category_id):
      form = ContentForm()
      category = get_object_or_404(Category, pk=category_id)
  
      if request.method == 'POST':
          form = ContentForm(request.POST)
  
          if form.is_valid():
  
              content = Content()
              content content_code = form.cleaned_data['content_code']
              content.product_versions = form.cleaned_data['product_versions']
              content.category = category
              content.creator = request.user
  
              content.save()
  
              return HttpResponseRedirect(reverse('category-detail', args=(category.id, )))
  
      return render_to_response('add_content.html', {
              'form': form,
              'category': category,
          }, context_instance=RequestContext(request))
  </code></pre>
  
  <p>urls</p>
  
  <pre><code>url(r'^/add-content/(\d+)/$', 'app1.views.add_content', name='add_content'),
  </code></pre>
  
  <p>in template i have error in this line</p>
  
  <pre><code>&lt;a id="add_content" class="button" href="{% url 'app1.views.add_content' pk %}"&gt;Add New Content&lt;/a&gt;
  </code></pre>
  
  <p>What is the problem?</p>