Fatal error: OOUI\Exception: OOUI\Theme::singleton was called with no singleton theme set. in C:\xampp\htdocs\wiki\vendor\oojs\oojs-ui\php\Theme.php:31 Stack trace: #0 C:\xampp\htdocs\wiki\vendor\oojs\oojs-ui\php\Element.php(259): OOUI\Theme::singleton() #1 C:\xampp\htdocs\wiki\vendor\oojs\oojs-ui\php\Tag.php(510): OOUI\Element->toString() #2 C:\xampp\htdocs\wiki\extensions\VisualEditor\includes\Hooks.php(252): OOUI\Tag->__toString() #3 C:\xampp\htdocs\wiki\includes\HookContainer\HookContainer.php(159): MediaWiki\Extension\VisualEditor\Hooks->onTextSlotDiffRendererTablePrefix(Object(TextSlotDiffRenderer), Object(MediaWiki\Context\RequestContext), Array) #4 C:\xampp\htdocs\wiki\includes\HookContainer\HookRunner.php(1336): MediaWiki\HookContainer\HookContainer->run('TextSlotDiffRen...', Array) #5 C:\xampp\htdocs\wiki\includes\diff\TextSlotDiffRenderer.php(278): MediaWiki\HookContainer\HookRunner->onTextSlotDiffRendererTablePrefix(Object(TextSlotDiffRenderer), Object(MediaWiki\Context\RequestContext), Array) #6 C:\xampp\htdocs\wiki\includes\diff\DifferenceEngine.php(1048): TextSlotDiffRenderer->getTablePrefix(Object(MediaWiki\Context\RequestContext), Object(MediaWiki\Title\Title)) #7 C:\xampp\htdocs\wiki\includes\diff\DifferenceEngine.php(1028): DifferenceEngine->showTablePrefixes() #8 C:\xampp\htdocs\wiki\includes\page\Article.php(1004): DifferenceEngine->showDiffPage(false) #9 C:\xampp\htdocs\wiki\includes\page\Article.php(503): Article->showDiffPage() #10 C:\xampp\htdocs\wiki\includes\actions\ViewAction.php(78): Article->view() #11 C:\xampp\htdocs\wiki\includes\actions\ActionEntryPoint.php(733): ViewAction->show() #12 C:\xampp\htdocs\wiki\includes\actions\ActionEntryPoint.php(510): MediaWiki\Actions\ActionEntryPoint->performAction(Object(Article), Object(MediaWiki\Title\Title)) #13 C:\xampp\htdocs\wiki\includes\actions\ActionEntryPoint.php(145): MediaWiki\Actions\ActionEntryPoint->performRequest() #14 C:\xampp\htdocs\wiki\includes\MediaWikiEntryPoint.php(199): MediaWiki\Actions\ActionEntryPoint->execute() #15 C:\xampp\htdocs\wiki\index.php(58): MediaWiki\MediaWikiEntryPoint->run() #16 {main} in C:\xampp\htdocs\wiki\vendor\oojs\oojs-ui\php\Tag.php on line 512