def _get_override_lookup_session(self):
        """Gets the AuthorizationLookupSession for the override typed Vault

        Assumes only one

        """
        from ..utilities import OVERRIDE_VAULT_TYPE
        try:
            override_vaults = self._get_vault_lookup_session().get_vaults_by_genus_type(OVERRIDE_VAULT_TYPE)
        except Unimplemented:
            return None
        if override_vaults.available():
            vault = override_vaults.next()
        else:
            return None
        session = self._get_authz_manager().get_authorization_lookup_session_for_vault(vault.get_id())
        session.use_isolated_vault_view()
        return session
Gets the AuthorizationLookupSession for the override typed Vault

        Assumes only one