$name = $this->prefixFieldName($name) . '[__identity]';
The problem with this line is that if this lookup resorts to an empty string, fluid will fail during a security check:
#1255072832: The form field name "[__identity]" is invalid. Reason: "" used not as last argument. Tx_Extbase_Security_Exception_InvalidArgumentForRequestHashGeneration thrown in file W:\TYPO3Winstaller\htdocs\Dummy\typo3\sysext\extbase\Classes\Security\Channel\RequestHashService.php in line 94.
I'm pretty sure that a mistake of mine led to renderHiddenIdentityField behaving this way, yet I don't see the point in creating misleading & invalid output.
Updated by Patrick Schriner about 10 years ago
okay, I found the reason - this happens when FormViewHelper->getFormObjectName() returns null; This happens when name is not set (which should not happen).
Still I think it could be less misleading if an error on this missing piece of configuration were raised.