Case C-306/18: Judgment of the Court (Eighth Chamber) of 15 May 2019 (request for a preliminary ruling from the Krajský soud v Ostravě — pobočka v Olomouci — Czech Republic) — KORADO a.s. v Generální ředitelství cel (Reference for a preliminary ruling — Common Customs Tariff — Tariff classification — Combined Nomenclature — Welded steel parts — Radiators for central heating, not electrically heated — Headings 7307 and 7322 — Concepts of radiator ‘parts’ and ‘tube or pipe fittings’ — Implementing Regulation (EU) 2015/23 — Validity)