[BUGFIX] Set correct default value for page action callbacks

This patch sets the correct default value for page action callbacks passed
for `TYPO3/CMS/Backend/PageActions`. Empty strings are not treated
properly, also the argument of `PageRenderer::loadRequireJsModule` sets
the default value to null.

Resolves: #88649
Related: #88532
Releases: master, 9.5
Change-Id: Ic5ce5eca5c0f2845ff9453e5f8d50de7cd650356
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61409
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>

typo3/sysext/backend/Classes/View/PageLayoutView.php

@@ -842,7 +842,7 @@ public function getTable_tt_content($id)
         $pageRenderer->loadRequireJsModule('TYPO3/CMS/Backend/LayoutModule/DragDrop');
         $pageRenderer->loadRequireJsModule('TYPO3/CMS/Backend/Modal');
         $pageRenderer->loadRequireJsModule('TYPO3/CMS/Backend/LayoutModule/Paste');
-        $pageActionsCallback = '';
+        $pageActionsCallback = null;
         if ($this->isPageEditable()) {
             $languageOverlayId = 0;
             $pageLocalizationRecord = BackendUtility::getRecordLocalization('pages', $this->id, (int)$this->tt_contentConfig['sys_language_uid']);

typo3/sysext/recordlist/Classes/Controller/RecordListController.php

@@ -258,7 +258,7 @@ protected function main(ServerRequestInterface $request)
         $this->getPageRenderer()->loadRequireJsModule('TYPO3/CMS/Backend/AjaxDataHandler');
         $calcPerms = $backendUser->calcPerms($this->pageinfo);
         $userCanEditPage = $calcPerms & Permission::PAGE_EDIT && !empty($this->id) && ($backendUser->isAdmin() || (int)$this->pageinfo['editlock'] === 0);
-        $pageActionsCallback = '';
+        $pageActionsCallback = null;
         if ($userCanEditPage) {
             $pageActionsCallback = 'function(PageActions) {
                 PageActions.setPageId(' . (int)$this->id . ');