Fatal error: PHP notice in file /www/htdocs/v084149/crohn-forum/lib/form/KniffelpForm.class.php (1323): Uninitialized string offset: 0

Information:

error message: PHP notice in file /www/htdocs/v084149/crohn-forum/lib/form/KniffelpForm.class.php (1323): Uninitialized string offset: 0
error code: 0
file: /www/htdocs/v084149/crohn-forum/wcf/lib/system/WCF.class.php (255)
php version: 5.6.38-nmm2
wcf version: 1.0.11 pl 3 (Horizon)
date: Mon, 01 Jun 2020 15:15:31 +0000
request: /crohn-forum/index.php?form=kniffelp&action=kniffel
referer:

Stacktrace:

#0 /www/htdocs/v084149/crohn-forum/lib/form/KniffelpForm.class.php(1323): WCF::handleError(8, 'Uninitialized s...', '/www/htdocs/v08...', 1323, Array)
#1 /www/htdocs/v084149/crohn-forum/lib/form/KniffelpForm.class.php(887): KniffelpForm->ermitteln('')
#2 /www/htdocs/v084149/crohn-forum/wcf/lib/page/AbstractPage.class.php(35): KniffelpForm->readParameters()
#3 /www/htdocs/v084149/crohn-forum/wcf/lib/util/RequestHandler.class.php(63): AbstractPage->__construct()
#4 /www/htdocs/v084149/crohn-forum/wcf/lib/util/RequestHandler.class.php(94): RequestHandler->__construct('kniffelp', Array, 'form')
#5 /www/htdocs/v084149/crohn-forum/index.php(8): RequestHandler::handle(Array)
#6 {main}