Steps to reproduce the issue

• Extension with display of sidebars
• Updated Joomla 4.0 with nightly build used "Joomla_4.0.0-beta1-dev-Development-Update_Package.zip Wednesday, 29 April 2020 02:00:24 UTC"

Expected result

• Sidebar still displaying

Actual result

An error has occurred. "Class 'Joomla\CMS\HTML\Helpers\stdClass' not found"
-> Location JROOT\libraries\src\HTML\Helpers\Sidebar.php:57

System information (as much as possible)

win10, XAMPP, PHP Version 7.3.9

Additional comments

I try to rewrite my "old" component rsgallery2 for j!4. I have used the code for the sidebbbars like in j!3. J4 showed the sidebars until last update.