It all depends on how you want / expect this to operate. If you decide `null` will be the value for this to trigger then `=== null` will do.

My concern is that an operant in an assertion is an explicit statement, even more so when using the triple equality operant. So `!== undefined` means that you can have pretty much any type / value there except undefined... we don't meant that...

I think locking the value to `null` so your mechanism will trigger is a good choice. Maybe better define that on the docs?