Contract Nullity Based on Mistake Regarding Essential Quality of Object

A lower court judgment was challenged regarding a contract dispute where a party alleged a unilateral declaration of will was invalid due to a mistake concerning the object of the obligation, which was a specific piece of property. The reviewing court upheld the lower court's decision, reasoning that for a mistake to invalidate a contract under civil law, it must relate to a quality of the object that was expressly or implicitly considered by the contracting parties as essential to their consent; since the specific quality alleged to be mistaken by the appellant was not established as a motive for the contract's formation, the claim of nullity based on mistake was correctly rejected.