(1) No act done or proceedings taken under this Act shall be questioned on the ground merely of-
(a) the existence of any vacancy in or any defect in the constitution, of the Board or any planning authority;
(b) any person having ceased to be a member of the Board or any planning authority;
(c) any person associated with any planning authority under section 14 having voted in contravention of the said section; or
(d) the failure to serve a notice on any person, where no substantial injustice has resulted from such failure; or
(e) any omission, defect or irregularity not affecting the merits of the case.
(2) Every meeting of the Board or any planning authority, the minutes of the proceedings of which have been duly signed as prescribed shall be taken to have been duly convened and to be free from all defects and irregularities.