presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorSessionProperties.java/RaptorSessionProperties/getExternalBatchId
class RaptorSessionProperties:    public static Optional<String> getExternalBatchId(ConnectorSession session)
    {
        return Optional.ofNullable(session.getProperty(EXTERNAL_BATCH_ID, String.class));
    }