At the time of separation from State service, an employee, such employee's estate or beneficiary, as the case may be, shall be compensated in cash for overtime credits not in excess of 30 days accrued and unused as of the effective date of separation; and further, except where provision is made for the transfer of leave credits, the employee shall be compensated in cash for vacation credits not in excess of 30 days accrued and unused as of the effective date of separation, except that in the case of resignation, the appointing authority may require, as a condition for such payment, that written notice of such resignation be given to the appointing authority at least two weeks prior to the last day of work. No employee who is removed from State service as a result of disciplinary action, or who resigns after charges of incompetency or misconduct have been served, shall be entitled to compensation for vacation credits under the provisions of this Part.