21. VACANCIES ETC., NOT TO INVALIDATE PROCEEDINGS OF THE BOARDS. - No act or proceeding of a Board shall be invalid merely by reason of- (a) any vacancy in, or any defect in the constitution of, the Board; or

(b) any defect in the appointment of a person acting as a member of the Board; or

(c) any irregularity in the procedure of the Board not affecting the merits of the case.