Joined Cases C-250/14 and C-289/14: Judgment of the Court (First Chamber) of 23 December 2015 (request for a preliminary ruling from the Conseil d’État — France) — Air France-KLM, formerly Air France (C-250/14), Hop!-Brit Air SAS, formerly Brit Air (C-289/14) v Ministère des Finances et des Comptes publics (VAT — Chargeable event and chargeability — Air transport — Ticket purchased but not used — Provision of the transport service — Issue of the ticket — Time of payment of the tax)