11. No suit, defence or exception, founded upon the omission of any formality, even imperative, in any act of the council or of an officer or employee of the municipality, shall prevail, unless the omission has caused actual prejudice or it be of a formality whose omission, according to the provisions of the law, would render null the proceeding from which it was omitted.
R. S. 1964, c. 193, s. 8; 1968, c. 55, s. 5.