--------------
CREATE PROCEDURE `pbl_assert_append_only`(
    IN p_table VARCHAR(64), IN p_priv VARCHAR(16), IN p_detail VARCHAR(255))
    READS SQL DATA
BEGIN
    IF p_table <> 'pbl_runtime_event' THEN
        RETURN;                       
    END IF;
    IF IFNULL(@pbl_guard_ctx, '') = 'append_only_admin' THEN
        RETURN;                       
    END IF;
    SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'PBL_APPEND_ONLY_DENIED',
            MYSQL_ERRNO = 45001;
END
--------------

ERROR 1064 (42000) at line 65: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ';                       
    END IF;
    IF IFNULL(@pbl_guard_ctx, '') = 'app...' at line 6