Steps to reproduce:

1. Create any Page Builder block that contains attribute of type 'richtext' or edit the vendor one by adding the following validator:

                   validators:
                       not_blank_richtext:
                           message: You must provide text
   
   

2. Add block from the type described above, don't add anything to the richtext field and save.

Result:
There is a JS error in a console:

Uncaught TypeError: Cannot read properties of null (reading 'value')

Expected result:
There should be no JS exception. Refreshing the page leaves Page Builder broken.

Note:
It looks like the JS issue doesn't affect validation, it seems to work correctly.