Case C-315/17: Order of the Court (Sixth chamber) of 22 March 2018 (request for a preliminary ruling from the Juzgado Contencioso-Administrativo No 2 de Zaragoza — Spain) — Pilar Centeno Meléndez v Universidad de Zaragoza (Reference for a preliminary ruling — Directive 1999/70/EC — Framework agreement on fixed-term work concluded by ETUC, UNICE and CEEP — Clause 4 — Principle of non-discrimination — Rules for horizontal career progression — Grant of remuneration supplement — National legislation excluding non-established civil servants — Definition of ‘employment conditions’ and ‘objective reasons’)