Fatal error: PHP error in file /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/UserGuestbookPage.class.php (111): Non-static method UserGuestbookData::getStats() should not be called statically

Information:

error message: PHP error in file /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/UserGuestbookPage.class.php (111): Non-static method UserGuestbookData::getStats() 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: 7.3.7
wcf version: 1.0.11 pl 1 (Horizon)
date: Fri, 19 Jul 2019 14:14:46 +0000
request: /index.php?page=UserGuestbook&userID=3&s=10cb6422dbd006bf1a8b7f11991328655d4589ec
referer:

Stacktrace:

#0 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/UserGuestbookPage.class.php(111): WCF::handleError(8192, 'Non-static meth...', '/mnt/web019/d1/...', 111, Array)
#1 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/AbstractPage.class.php(74): UserGuestbookPage->readData()
#2 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/UserGuestbookPage.class.php(185): AbstractPage->show()
#3 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/AbstractPage.class.php(36): UserGuestbookPage->show()
#4 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/page/UserGuestbookPage.class.php(29): AbstractPage->__construct()
#5 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/util/RequestHandler.class.php(63): UserGuestbookPage->__construct()
#6 /mnt/web019/d1/58/51859358/htdocs/Forum/wcf/lib/util/RequestHandler.class.php(91): RequestHandler->__construct('UserGuestbookPa...', Array, 'page')
#7 /mnt/web019/d1/58/51859358/htdocs/Forum/index.php(8): RequestHandler::handle(Array)
#8 {main}