Case T-518/16: Judgment of the General Court of 4 December 2018 — Carreras Sequeros and Others v Commission (Civil service — Officials and members of the contractual staff — Reform of the Staff Regulations of 1 January 2014 — Article 6 of Annex X to the Staff Regulations — New provisions relating to annual leave applicable to officials posted in a third country — Objection of illegality — Purpose of annual leave)