Canonical way of marking a buf local var to be safe if nil/t?

[Kaushal Modi]

Hi,

What would be a canonical way (if any) of setting a var to be a safe buffer
local variable as long as its value is either nil or t?

I use

(put 'my-foo-var 'safe-local-variable (lambda (val) (or (equal val nil)
(equal val t))))
-- 

-- 
Kaushal Modi