2. Where an agreement relative to a sabbatical with deferred salary between a person and his employer becomes null, the pensionable salary, credited service and contributions in respect of a year of leave or part of a year of leave shall be determined, for the purposes of the retirement plan to which he contributes, as follows:
(1) the salary paid to the person shall be deemed to be non-pensionable salary;
(2) no year of service or part of a year of service shall be credited;
(3) subject to section 4, the contributions paid by the person shall be deemed to be overpayments within the meaning of the retirement plan to which he contributes.