Failed include handling & content parsing on PHP 8.3

[ssddanbrown]

Seems to be a recent issue, started to appear in tests.
Occurs on my dev instance using 8.3.14.
Occurs in actual use too, not just tests.

Need to understand when this started, why, and if the issue is with our code or a PHP bug.

Error detail

Details

Call to a member function importNode() on null
Stack Trace

#0 /home/dan/web/bookstack/app/Entities/Tools/PageIncludeParser.php(56): BookStack\Entities\Tools\PageIncludeParser->replaceNodeWithNodes()
#1 /home/dan/web/bookstack/app/Entities/Tools/PageContent.php(310): BookStack\Entities\Tools\PageIncludeParser->parse()
#2 /home/dan/web/bookstack/app/Entities/Controllers/PageController.php(153): BookStack\Entities\Tools\PageContent->render()
#3 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Routing/Controller.php(54): BookStack\Entities\Controllers\PageController->show()
#4 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Routing/ControllerDispatcher.php(43): Illuminate\Routing\Controller->callAction()
#5 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Routing/Route.php(259): Illuminate\Routing\ControllerDispatcher->dispatch()
#6 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Routing/Route.php(205): Illuminate\Routing\Route->runController()
#7 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Routing/Router.php(806): Illuminate\Routing\Route->run()
#8 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(144): Illuminate\Routing\Router->Illuminate\Routing\{closure}()
#9 /home/dan/web/bookstack/app/Http/Middleware/Authenticate.php(23): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#10 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(183): BookStack\Http\Middleware\Authenticate->handle()
#11 /home/dan/web/bookstack/app/Http/Middleware/Localization.php(32): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#12 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(183): BookStack\Http\Middleware\Localization->handle()
#13 /home/dan/web/bookstack/app/Http/Middleware/RunThemeActions.php(26): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#14 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(183): BookStack\Http\Middleware\RunThemeActions->handle()
#15 /home/dan/web/bookstack/app/Http/Middleware/CheckEmailConfirmed.php(47): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#16 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(183): BookStack\Http\Middleware\CheckEmailConfirmed->handle()
#17 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/VerifyCsrfToken.php(78): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#18 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(183): Illuminate\Foundation\Http\Middleware\VerifyCsrfToken->handle()
#19 /home/dan/web/bookstack/vendor/laravel/framework/src/Illuminate/View/Middleware/ShareErrorsFromSession.php(49): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()

Reduced Example Case

https://3v4l.org/BQFa7

[ssddanbrown]

Only occurs on PHP 8.3.14.
Potentially a PHP bug, have raised here: php/php-src#16967
Is something we can easily work around though, so something we can add into a patch release for PHP 8.3.14 users.

[ssddanbrown]

Due to be addressed in PHP 8.3.15, reference: php/php-src#16967 (comment)