Case C-935/19: Judgment of the Court (Ninth Chamber) of 15 April 2021 (request for a preliminary ruling from the Wojewódzki Sąd Administracyjny we Wrocławiu — Poland) — Grupa Warzywna sp. z o.o. v Dyrektor Izby Administracji Skarbowej we Wrocławiu (Reference for a preliminary ruling — Common system of value added tax (VAT) — Directive 2006/112/EC — Article 273 — Overstatement in the tax return of the amount of the refund of VAT — Error of assessment by the taxable person concerning the taxable nature of a transaction — Correction of the tax return following an audit — Penalty of an amount equal to 20 % of the overstated VAT reimbursement — Principle of proportionality)