Judgment of the Court of First Instance (First Chamber) of 21 April 2004 in Case T-172/01 M v Court of Justice of the European Communities (Spouse divorced from a former member of a Community institution, since deceased — Maintenance — Verbal agreement between the former spouses — Law applicable to the formal requirements for the agreement and the admissibility of the means of proving its existence (Article 27 of Annex VIII to the Staff Regulations of the European Communities))