Case C-720/19: Judgment of the Court (Sixth Chamber) of 21 October 2020 (request for a preliminary ruling from the Verwaltungsgericht Düsseldorf — Germany) — GR v Stadt Duisburg (Reference for a preliminary ruling — EEC-Turkey Association Agreement — Decision No 1/80 — Article 7, first paragraph — Right of residence of family members of a Turkish worker legally employed in a Member State — Naturalisation of the family member concerned in the host Member State — Maintenance of the right of residence — Acquired rights)