TYPO3 Core

This exception occures in error log:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: rawurlencode() expects parameter 1 to be string, null given | TypeError thrown in file /var/www/public/typo3/sysext/backend/Classes/Controller/Wizard/NewContentElementWizardController.php in line 283.

how to reproduce:
in any given page, put following PageTS:

mod.wizards.newContentElement.wizardItems {
    common.header >
}

or

mod.wizards.newContentElement.wizardItems {
    common.header = LLL:EXT:bootstrap_package/Resources/Private/Language/Backend.xlf:someNotAvailableLabelString
}

and use the new content element wizard afterwards.