code: def queryset(self, request, queryset):
          
          if self.value():
              try:
                  section = SectionPage.objects.get(id=self.value())
                  return queryset.child_of(section).all()
              except (ObjectDoesNotExist, MultipleObjectsReturned):
                  return None
docs: Returns the filtered queryset based on the value
          provided in the query string and retrievable via
          `self.value()`.