論法律行為有效性與稅捐債務之連動──以最高行政法院109年度上字第699號判決及最高行政法院109年度判字第449號判決為中心【學習式判解評析】 The Linkage between Juridical Act Effectiveness and Taxation Obligation: Focusing on the Supreme Administrative Court Judgment (109) Shang Tzu No. 699 and the Supreme Administrative Court Judgment (109) Pan Tzu No. 449