102.—Every instrument (being an assignment of, a charge on, or an agreement to assign or charge any pay, allowance, gratuity or grant) made by a member of the Defence Forces shall be void except—

(a) it is made, in pursuance of any regulation made in this behalf by the Minister, for the benefit of the family (including an illegitimate child) of that member, or

(b) it is authorised by subsection (2) of section 100 or by an Act of the Oireachtas.