Case C-107/19: Judgment of the Court (Tenth Chamber) of 9 September 2021 (request for a preliminary ruling from the Obvodní soud pro Prahu 9 — Czech Republic — XR v Dopravní podnik hl. m. Prahy, akciová společnost (Reference for a preliminary ruling — Social policy — Directive 2003/88/EC — Organisation of working time — Concepts of ‘working time’ and ‘rest period’ — Break during which the employee must remain ready to respond to a call-out within a two-minute time limit — Primacy of EU law)