California Code, Probate Code - PROB § 1260

(a) If notice of a hearing is required, proof of giving notice of the hearing shall be made to the satisfaction of the court at or before the hearing.

(b) If it appears to the satisfaction of the court that notice has been regularly given or that the party entitled to notice has waived it, the court shall so find in its order.

(c) The finding described in subdivision (b), when the order becomes final, is conclusive on all persons.