TYPO3 Core

If you start editing a inline record (flexform) in the backend, you will get a ajax call with a error 500 - Internal Server Error.

Reproducing the bug:
Install the extension "styleguide", create the default page and item structure.
Go to the "user settings", then open the tab "Edit and Advanced functions" and clear the "user settings" with the button "Reset Configuration and Clear Temporary Data".

Then click on the list module and the page "flex". You will see a item in the table "Form engine - flex (1)". Click on the edit button, go to the tab "inline" and start editing the item. You will see a flash message overlay with the message "error 500".

Stack trace:
Request: htzp://domain.local/typo3/index.php?ajaxID=%2Fajax%2Frecord%2Finline%2Fexpandcollapse&ajaxToken=...

Uncaught TYPO3 Exception
unserialize() expects parameter 1 to be string, null given

TypeError thrown in file
/typo3/sysext/backend/Classes/Controller/FormInlineAjaxController.php in line 802.

/var/www/typo3Core/typo3/sysext/backend/Classes/Controller/FormInlineAjaxController.php:

00800:     {
00801:         $backendUser = $this->getBackendUserAuthentication();

00802:         $inlineView = unserialize($backendUser->uc['inlineView']);

00803:         if (!is_array($inlineView)) {
00804:             $inlineView = array();