Case C-256/07: Judgment of the Court (Second Chamber) of 19 March 2009 (reference for a preliminary ruling from the Finanzgericht Düsseldorf (Germany)) — Mitsui & Co. Deutschland GmbH v Hauptzollamt Düsseldorf (Community Customs Code — Repayment of customs duties — Article 29(1) and (3)(a) — Value for customs purposes — Regulation (EEC) No 2454/93 — Article 145(2) and (3) — Taking into account, for customs valuation purposes, of payments made by the seller in performance of a warranty obligation provided for in the contract of sale — Temporal application — Substantive rules — Procedural rules — Retroactive application of a rule — Validity)