In the RestoreRegisterContentObject::render method a call
to array_pop is performed. The result is assigned to the
variable $frontendController->register which has type array.
However array_pop can return null, this patch add's a
null coalesce operator to ensure that correct type.

Resolves: #104495
Releases: main, 12.4, 11.5
Change-Id: I46efce10e4322ff3cd39b5a0eeafd1f768644e38
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85404


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>