docs: def _closure_deletelink(self, oldparentpk):
          """Remove incorrect links from the closure tree."""
          self._closure_model.objects.filter(
              **{
                  "parent__%s__child" % self._closure_parentref(): oldparentpk,
                  "child__%s__parent" % self._closure_childref(): self.pk
              }
          ).delete()