Case C-702/17: Judgment of the Court (First Chamber) of 21 March 2019 (request for a preliminary ruling from the Consiglio di Stato — Italy) — Unareti SpA v Ministero dello Sviluppo Economico and Others (Reference for a preliminary ruling — Internal market in natural gas — Public service distribution concessions — Early cessation of concessions at the end of a transitional period — Reimbursement by the incoming concessionaire to the outgoing concessionaire — Principle of legal certainty)