[BUGFIX] Check if property is null

ObjectAccess::getPropertyPath requires its second parameter to be string,
so it should not be called if the property argument is null
but return null instead as the getPropertyPath method would have done
in earlier versions.

Resolves: #93798
Releases: master, 10.4
Change-Id: I35ff131e1819c0fbb3bc98c8dc5a0a53d799daae
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68556
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Richard Haeser <richard@richardhaeser.com>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Richard Haeser <richard@richardhaeser.com>

typo3/sysext/fluid/Classes/ViewHelpers/Form/AbstractFormFieldViewHelper.php

@@ -296,6 +296,9 @@ protected function addAdditionalIdentityPropertiesIfNeeded()
      */
     protected function getPropertyValue()
     {
+        if ($this->arguments['property'] === null) {
+            return null;
+        }
         $viewHelperVariableContainer = $this->renderingContext->getViewHelperVariableContainer();
         if (!$viewHelperVariableContainer->exists(
             FormViewHelper::class,