12. (1) Any member of the Council may, at any time, resign his membership by writing under his hand addressed to the President, and the office of such member shall be deemed to have fallen vacant from the date of acceptance of his resignation by the President. (2) The President may, at any time, resign his office by writing under his hand addressed to the Government, and the office of the President including his membership of the Council shall be deemed to have fallen vacant from the date of acceptance of his resignation by the Government. (3) A member of the Council shall be deemed to have vacated his seat if he absents himself, without sufficient excuse, from three consecutive meetings of the Council, or if his name is, for any cause, removed from the Register under section 20, or remains out of Bangladesh for a continuous period exceeding one year. (4) A casual vacancy in the Council shall be filled by election, or by nomination, as the case may be, and the person elected or nominated to fill the vacancy shall hold office for the remaining period of the duration of the Council: Provided that no election shall be held or no nomination shall be made to fill a casual vacancy occurring within six months prior to the date of the expiry of the duration of the Council, but such a vacancy may be filled by co-option by the Council. (5) No act done by the Council shall be called in question on the ground merely of the existence of any vacancy in, or defect in the Constitution of, the Council.