Case C-35/19: Judgment of the Court (Eighth Chamber) of 24 October 2019 (Request for a preliminary ruling from the Tribunal de première instance de Liège — Belgium) — BU v État belge (Reference for a preliminary ruling — Free movement of workers — Equal treatment — Income tax — National legislation — Tax exemption for disability allowances — Allowances received in another Member State — Not included — Difference in treatment)