title: Using get_queryset() in ViewSets, can't access the Detail Views. Error: Cannot use None as a query value
body: <p>When I do a DELETE request to <code>127.0.0.1:8000/tasks/10/</code>, I get the error that Cannot use None as a query value.</p>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>class TaskViewSet(viewsets.ModelViewSet):
      def get_queryset(self):
          p1 = self.request.query_params.get('parameter')    
          queryset = Task.objects.nearby(p1)    
          return queryset
  
      serializer_class = TaskSerializer
  </code></pre>
  
  <p><strong>urls.py</strong></p>
  
  <pre><code>task_list = views.TaskViewSet.as_view({
      'get': 'list',
      'post': 'create'
  })
  task_detail = views.TaskViewSet.as_view({
      'get': 'retrieve',
      'put': 'update',
      'patch': 'partial_update',
      'delete': 'destroy'
  })
  
  # The API URLs are now determined automatically by the router.
  urlpatterns = [
      url(r'^', include(router.urls)),
      url(r'^tasks/$', task_list, name='task-list'),
      url(r'^tasks/(?P&lt;pk&gt;[0-9]+)/$', task_detail, name='task-detail'),
  ]
  </code></pre>
  
  <p>Everything works fine for list e.g. all requests to <code>127.0.0.1:8000/tasks/</code>. However, none of the request work for the detail views. I'm assuming it's something to do with the <code>get_queryset()</code>.</p>