def METHOD_NAME(self, feature):
    if feature.get("area_code") == "CED":
        return "unit_id:" + str(feature.get("unit_id"))
    if feature.get("code") == "999999999":
        raise ValueError(
            "Expected GSS code but found {code} for feature: ({type} - {name})".format(
                code=feature.get("code"),
                type=feature.get("area_code"),
                name=feature.get("name"),
            )
        )
    return "gss:" + feature.get("code")