Fatal error: PHP error in file /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/CustomPage.class.php (44): Non-static method CustomPageEditor::getChildPages() should not be called statically

Information:

error message: PHP error in file /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/CustomPage.class.php (44): Non-static method CustomPageEditor::getChildPages() should not be called statically
error code: 0
file: /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/system/WCF.class.php (255)
php version: 7.3.12
wcf version: 1.0.11 pl 1 (Horizon)
date: Wed, 11 Dec 2019 10:57:16 +0000
request: /index.php?page=Custom&pageID=1
referer:

Stacktrace:

#0 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/CustomPage.class.php(44): WCF::handleError(8192, 'Non-static meth...', '/mnt/web019/d1/...', 44, Array)
#1 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/AbstractPage.class.php(74): CustomPage->readData()
#2 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/CustomPage.class.php(74): AbstractPage->show()
#3 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/AbstractPage.class.php(36): CustomPage->show()
#4 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/util/RequestHandler.class.php(63): AbstractPage->__construct()
#5 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/util/RequestHandler.class.php(91): RequestHandler->__construct('CustomPage', Array, 'page')
#6 /mnt/web019/d1/58/51859358/htdocs/Forum/index.php(8): RequestHandler::handle(Array)
#7 {main}