Cannot edit templates in 1.35

[The-Foilist]

This is using the current master branch with MW 1.35. I can create infobox templates normally, but attempting to submit an edit to an infobox template that already exists results in the following error:

[545e4e5eff1832cfec85469a] /index.php?title=Template:Character&action=submit TypeError from line 1007 of /var/www/mediawiki/includes/parser/Parser.php: Return value of Parser::getTitle() must be an instance of Title, null returned

Backtrace
#0 /var/www/mediawiki/includes/parser/PPFrame_Hash.php(71): Parser->getTitle()
#1 /var/www/mediawiki/includes/parser/Preprocessor_Hash.php(58): PPFrame_Hash->__construct()
#2 /var/www/mediawiki/extensions/PortableInfobox/includes/services/Helpers/PortableInfoboxParsingHelper.php(31): Preprocessor_Hash->newFrame()
#3 /var/www/mediawiki/extensions/PortableInfobox/includes/services/PortableInfoboxDataService.php(199): PortableInfobox\Helpers\PortableInfoboxParsingHelper->parseIncludeonlyInfoboxes()
#4 /var/www/mediawiki/extensions/PortableInfobox/includes/PortableInfobox.hooks.php(45): PortableInfoboxDataService->reparseArticle()
#5 /var/www/mediawiki/includes/HookContainer/HookContainer.php(320): PortableInfoboxHooks::onPageContentSave()
#6 /var/www/mediawiki/includes/HookContainer/HookContainer.php(131): MediaWiki\HookContainer\HookContainer->callLegacyHook()
#7 /var/www/mediawiki/includes/HookContainer/HookRunner.php(2788): MediaWiki\HookContainer\HookContainer->run()
#8 /var/www/mediawiki/includes/Storage/PageUpdater.php(768): MediaWiki\HookContainer\HookRunner->onPageContentSave()
#9 /var/www/mediawiki/includes/page/WikiPage.php(2015): MediaWiki\Storage\PageUpdater->saveRevision()
#10 /var/www/mediawiki/includes/EditPage.php(2456): WikiPage->doEditContent()
#11 /var/www/mediawiki/includes/EditPage.php(1723): EditPage->internalAttemptSave()
#12 /var/www/mediawiki/includes/EditPage.php(680): EditPage->attemptSave()
#13 /var/www/mediawiki/includes/actions/EditAction.php(71): EditPage->edit()
#14 /var/www/mediawiki/includes/actions/SubmitAction.php(38): EditAction->show()
#15 /var/www/mediawiki/includes/MediaWiki.php(527): SubmitAction->show()
#16 /var/www/mediawiki/includes/MediaWiki.php(313): MediaWiki->performAction()
#17 /var/www/mediawiki/includes/MediaWiki.php(940): MediaWiki->performRequest()
#18 /var/www/mediawiki/includes/MediaWiki.php(543): MediaWiki->main()
#19 /var/www/mediawiki/index.php(53): MediaWiki->run()
#20 /var/www/mediawiki/index.php(46): wfIndexMain()
#21 {main}

Special:Version
MediaWiki | 1.35.0
PHP | 7.4.3 (apache2handler)
MariaDB | 10.3.22-MariaDB-1ubuntu1
ICU | 66.1
Lua | 5.1.5

[The-Foilist]

I did some more testing, and it turns out that attempting to edit any page in the Template namespace throws the same error, even if there are no tags relating to PortableInfobox.