What is the effect of failing to file an affidavit?

' * * * the effect of failure to file the affidavit is merely to admit that the instrument pleaded is what it purports on its face to be; that the matters recited therein are true; and that it was executed and delivered by the parties who signed it, in the capacity in which they appear to have acted. A plaintiff * * * may still attack the instrument for any cause not going to its genuineness or due execution, and may, without further pleading, introduce competent evidence to sustain any other legitimate defense thereto, such as fraud, mistake, undue influence, * * *.' 21 Cal.Jur. 168; Donovan v. Security-First Nat. Bk., 67 Cal.App.2d 845, 852, 155 P.2d 856.