Error: Call to a member function getFileSetID() on null

I can’t edit any page in the website.
One week ago, when updating the website, these are the steps I followed:

Step 1: I went to Stacks and Blocks> Stacks

Step 1b: clicked on the assistance module and clicked on ‘edit block’

Step 2: opened the dropdown menu

Step 3: selected none

And that’s when I got the error

Not sure what to do here.

I appreciate it,

Version 8.4.4