Add "None of the Above" functionality to Entity Checkboxes

Problem/Motivation

I am working on a webform which uses entity checkboxes. My client really wants a "none of the above" option and I can see that that option is explicitly disabled for entity checkboxes. I cannot figure out why that was done when the "All of the above" option is available.

While it's kind of redundant, I think it should be available if site builders want to use it. If there's some solid reasoning behind why it's disabled, I'd love to hear it!