where the face expression evals to nil.
(add-text-properties start end (cddr val))
(setq val (cadr val)))
(cond
+ ((not val)
+ ;; If `val' is nil, don't do anything. It is important to do it
+ ;; explicitly, because when adding nil via things like
+ ;; font-lock-append-text-property, the property is actually
+ ;; changed from <face> to (<face>) which is undesirable. --Stef
+ nil)
((not override)
;; Cannot override existing fontification.
(or (text-property-not-all start end 'face nil)