The right to maintain and operate a nonconforming use shall terminate immediately when:
(a) A nonconforming use is substituted for a conforming use;
(b) A nonconforming use is substituted for another nonconforming use, contrary to the provisions of this Planning and Zoning Code;
(c) A false registration is filed or there is a failure to register in accordance with the provisions of Section 751.01; or
(d) A nonconforming use is vacant, not operated or not in use for a continuous period of six months or more. Intent to resume operation or use shall not affect this provision.