Case T-737/17: Judgment of the General Court of 30 April 2019 — Wattiau v Parliament (Civil service — Social Security — JSIS — Reimbursement of medical costs — Agreement concluded inter alia between the European Union, Luxembourg and the Entente des hôpitaux luxembourgeois on the scales of fees for hospital care received by JSIS members — Plea of illegality — Principle of non-discrimination on grounds of nationality — First paragraph of Article 18 TFEU — Articles 20 and 21 of the Charter of Fundamental Rights — Article 39 of the Joint rules on sickness insurance for officials)