Sym 3.0.0 - Fatal Error: Call to undefined method FrontendPage::registerPHPFunction()

[cylkee]

An error occurred in /path-redacted/extensions/xssfilter/extension.driver.php around line 97.

96         public static function FrontendParamsResolve(array &$context) {
97             Frontend::Page()->registerPHPFunction(array(

Backtrace
PHP 7.4.12

[/path-redacted/symphony/lib/toolkit/class.extensionmanager.php:754]
    Extension_XSSFilter::FrontendParamsResolve();
[/path-redacted/symphony/lib/toolkit/class.frontendpage.php:442]
    ExtensionManager::notifyMembers();
[/path-redacted/symphony/lib/toolkit/class.frontendpage.php:197]
    FrontendPage->__buildPage();
[/path-redacted/symphony/lib/core/class.frontend.php:105]
    FrontendPage->generate();
[/path-redacted/symphony/lib/boot/func.utilities.php:235]
    Frontend->display();
[/path-redacted/symphony/lib/boot/func.utilities.php:224]
    symphony_launcher();
[/path-redacted/index.php:16]
    symphony();

Database Query Log
MYSQL 10.3.27-MariaDB

[0.0002] SELECT SQL_CACHE VERSION();
[0.0001] SET time_zone = :value;
[0.0006] SHOW COLUMNS FROM `sym_extensions_delegates`
    LIKE :like;
[0.0005] SELECT SQL_CACHE `t1`.`name`, `t2`.`page`, `t2`.`delegate`, `t2`.`callback`, `t2`.`order`
    FROM `sym_extensions` AS `t1` INNER JOIN `sym_extensions_delegates` AS `t2` ON `t1`.`id` = `t2`.`extension_id`
    WHERE `t1`.`status` = :t1_status
    ORDER BY `t2`.`delegate` ASC, `t2`.`order` ASC, `t1`.`name` ASC;
[0.0003] SELECT SQL_CACHE `session_data`
    FROM `sym_sessions`
    WHERE `session` = :session
    LIMIT 1;
[0.0003] SELECT SQL_CACHE `a`.*
    FROM `sym_authors` AS `a`
    WHERE `a`.`username` = :a_username
    ORDER BY `a`.`id` ASC
    LIMIT 1;
[0.0016] UPDATE `sym_authors`
    SET `last_seen` = :last_seen
    WHERE `id` = :id;
[0.0004] SELECT SQL_CACHE `p`.*
    FROM `sym_pages` AS `p` INNER JOIN `sym_pages_types` AS `pt` ON `p`.`id` = `pt`.`page_id`
    WHERE `pt`.`type` = :pt_type
    ORDER BY `p`.`sortorder` ASC
    LIMIT 1;
[0.0003] SELECT SQL_CACHE `pt`.`type`
    FROM `sym_pages_types` AS `pt`
    WHERE `pt`.`page_id` = :pt_page_id
    GROUP BY `pt`.`type`
    ORDER BY `pt`.`type` ASC; 

Commit 4cae482 from PR #9 appears to fix it.