TYPO3 Core

Setting eval=null in tca.php of the extension now works in the Typo3 forms, but how can I change or set a value to NULL in my own extension.
Using
$this->tce = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('TYPO3\\CMS\\Core\\DataHandling\\DataHandler');
$this->tce->start($data,$cmd,$new_BE_USER);
$this->tce->process_cmdmap();
$this->tce->process_datamap();

where I got a "field" => null in the $data array wont work (sets the field to 0).

Currently I am manually deleting the value with an UPDATE statement, but thats not how its meant to be I guess. Looks like old code from the area before NULL was possible in number fields.