warning after overwriting get_form
<p>In my ClassBased Update/Create Views I added some classes:</p>

<pre><code>class IndexUpdateView(UpdateView):
    fields = '__all__'
    model = Index
    template_name = 'index_form.html'

    def get_success_url(self):
        return reverse('IndexList')

    def get_form(self, form_class):
        form = super(IndexUpdateView, self).get_form(form_class)
        form.fields['year'].widget.attrs.update({"class": "form-control tosp"})
        form.fields['index'].widget.attrs.update({"class": "form-control tosp"})
        return form
</code></pre>

<p>After adding the "get_form" I got the warning:</p>

<blockquote>
  <p>RemovedInDjango110Warning: <code>Index.views.IndexCreateView.get_form</code> method must define a default value for its <code>form_class</code> argument.</p>
</blockquote>

<p>How to define a default value?</p>