docs: def get_filter_form(self, **kwargs):
          """
          If there is a filter_form, initializes that
          form with the contents of request.GET and
          returns it.
          """
  
          form = None
          if self.filter_form:
              form = self.filter_form(self.request.GET)
          elif self.model and hasattr(self.model._meta, '_is_view'):
              form = VersionFilterForm(self.request.GET)
          return form