California Code, Code of Civil Procedure - CCP § 587

An application by a plaintiff for entry of default under subdivision (a),(b), or (c) of Section 585 or Section 586shall include an affidavit stating that a copy of the application has been mailed to the defendant's attorney of record or, if none, to the defendant at his or her last known address and the date on which the copy was mailed. If no such address of the defendant is known to the plaintiff or plaintiff's attorney, the affidavit shall state that fact.

No default under subdivision (a),(b), or (c) of Section 585 or Section 586 shall be entered, unless the affidavit is filed. The nonreceipt of the notice shall not invalidate or constitute ground for setting aside any judgment.