In the absence of fraud no error or mistake in the mailing of the notices, or any of them, and no failure of any property owners to receive the same shall in any way affect the validity of the proceedings, but the clerk shall file his affidavit of mailing such notice, and such affidavit shall be conclusive evidence that the notices have been mailed as required by this division.
Ca. Sts. and High. Code § 2855