The issue here is the order of execution of code like this (string)$array['key'] ?? ''. The intention is check the existence of the key via ?? but the cast (string) is executed before ??. At the end the check does not happen.
Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1476107295: PHP Warning: Undefined array key "header" in /l10nmgr_v11/packages/l10nmgr/Classes/View/L10nHtmlListView.php line 128 | TYPO3\CMS\Core\Error\Exception thrown in file /l10nmgr_v11/public/typo3/sysext/core/Classes/Error/ErrorHandler.php in line 137.
The issue here is the order of execution of code like this
(string)$array['key'] ?? ''. The intention is check the existence of the key via??but the cast(string)is executed before??. At the end the check does not happen.