[TASK] Code cleanup in DataHandler

Fix some IDE warnings in DataHandler class.

Resolves: #83170
Releases: master
Change-Id: I789ba23d2ff7fd9d1f96e7e9110c7be125f4de6e
Reviewed-on: https://review.typo3.org/54876


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>