§ 182. Vacancy, how filled. When a vacancy shall occur, otherwise than by expiration of term, in the office of police justice, the same shall be filled, for the balance of the unexpired term, at the next city election happening not less than thirty days after such vacancy occurs. Until such vacancy shall be so filled, the mayor may appoint a qualified attorney to fill the same, who shall hold office until the first day of January after the election at which his successor is elected.