Unity tweak tool: how to disable window switching shortcuts?

I found the "unity tweak tool" the other day, and today I played around a bit ... and today I wanted to make some adaptions for the task switcher.

There is a field for windows switcher shortcuts; and I am wondering: how on earth would I disable shortcuts?

Example: it says Start switcher for all Workspaces

I can now click on "" and it then says "New shortcut" ... but well, I dont want to set a shortcut. And I could not find a way to get it to show "Disabled" like it does for other entries.

Any idea how that would work?