rhx_gis string returned in the / query.

def root_rhx_gis(self) -> Optional[str]:
        """rhx_gis string returned in the / query."""
        if self.is_logged_in:
            # At the moment, rhx_gis seems to be required for anonymous requests only. By returning None when logged
            # in, we can save the root_rhx_gis lookup query.
            return None
        if not self._root_rhx_gis:
            self._root_rhx_gis = self.get_json('', {})['rhx_gis']
        return self._root_rhx_gis