Steps to reproduce

1. Install clean IBEXA DXP 3.2
2. create a custom block with attributes like here: https://doc.ibexa.co/en/3.2/extending/extending_page/#creating-custom-page-blocks
3. add a block to site 
4. remove any attribute from the custom block
5. try to preview/edit the site in Page Builder

Result:

An exception has been thrown during the rendering of a template ("Notice: Undefined index: name").

Expected result

Edit and preview mode work correctly