At the expiration of the terms of office, or if a vacancy occurs in either the office of Tax Assessor or the office of Tax Collector of Hale County before such date, then immediately upon the occurrence of such vacancy there shall be the office of county revenue commissioner in Hale County. If such office is established upon the occurrence of a vacancy in either the office of tax assessor or tax collector, then the tax assessor or tax collector, as the case may be, remaining in office shall be the county revenue commissioner for the remainder of the term for which he or she was elected tax assessor or tax collector, as the case may be. A revenue commissioner shall be elected at an election called for the purpose and every six years thereafter. He or she shall serve for a term of office of six years from the first day of the term next succeeding his or her election and until his or her successor is similarly elected, qualified, and takes office.