Internal error

[cec67f3f35de9718466edcd3] /w/index.php Error from line 204 of /var/www/liandri/w/extensions/CategoryTree/CategoryTreeFunctions.php: Call to undefined method Xml::escapeJsString()

Backtrace:

#0 /var/www/liandri/w/extensions/CategoryTree/CategoryPageSubclass.php(14): CategoryTree::setHeaders()
#1 /var/www/liandri/w/extensions/CategoryTree/CategoryPageSubclass.php(34): CategoryTreeCategoryViewer->getCategoryTree()
#2 /var/www/liandri/w/includes/CategoryViewer.php(385): CategoryTreeCategoryViewer->addSubcategoryObject()
#3 /var/www/liandri/w/includes/CategoryViewer.php(116): CategoryViewer->doCategoryQuery()
#4 /var/www/liandri/w/includes/page/CategoryPage.php(117): CategoryViewer->getHTML()
#5 /var/www/liandri/w/includes/page/CategoryPage.php(72): CategoryPage->closeShowCategory()
#6 /var/www/liandri/w/includes/actions/ViewAction.php(68): CategoryPage->view()
#7 /var/www/liandri/w/includes/MediaWiki.php(499): ViewAction->show()
#8 /var/www/liandri/w/includes/MediaWiki.php(293): MediaWiki->performAction()
#9 /var/www/liandri/w/includes/MediaWiki.php(862): MediaWiki->performRequest()
#10 /var/www/liandri/w/includes/MediaWiki.php(523): MediaWiki->main()
#11 /var/www/liandri/w/index.php(43): MediaWiki->run()
#12 {main}