Case C-72/18: Judgment of the Court (Second Chamber) of 20 June 2019 (request for a preliminary ruling from the Juzgado de lo Contencioso-Administrativo de Pamplona — Spain) — Daniel Ustariz Aróstegui v Departamento de Educación del Gobierno de Navarra (Reference for a preliminary ruling — Social policy — Directive 1999/70/EC — Framework agreement on fixed-term work concluded by ETUC, UNICE and CEEP — Clause 4(1) — Principle of non-discrimination — Public sector education — National provision granting particular additional remuneration only to teachers employed for an indefinite duration as established public officials — Exclusion of teachers employed under a fixed-term contract governed by public law — Concept of ‘objective grounds’ - Characteristics inherent in the status of established public official)