An officer who desires to resign shall submit his resignation to the Governor, whose action thereon shall be final. The Governor may refuse to accept a resignation when the officer is under investigation, under charges, awaiting result of trial, absent without leave, absent in the hands of civil authorities, in default with respect to State or Federal funds or property, in time of war or when war is imminent, in time of civil stress or emergency, or on account of the exigencies of the service.