TYPO3 Core

With the new Fluid based PageLayoutView, the preview rendering hook of ext:form fails:

htmlspecialchars() expects parameter 1 to be string, null given

in /var/www/html/typo3/sysext/form/Classes/Hooks/FormPagePreviewRenderer.php line 63
        array &$row
    ) {
        if ($row['CType'] === 'form_formframework') {
            $contentType = $parentObject->CType_labels[$row['CType']];
            $itemContent .= $parentObject->linkEditContent('<strong>' . htmlspecialchars($contentType) . '</strong>', $row) . '<br />';

            $flexFormData = GeneralUtility::makeInstance(FlexFormService::class)
                ->convertFlexFormContentToArray($row['pi_flexform']);