(1) Where the subject of a claim is designated in species only, and its quality cannot be determined by the nature of the juristic act or by the intention of the parties, the obligor is bound to perform with a thing of medium quality.
(2) If in the cases mentioned in the preceding paragraph the obligor has completed all acts that are necessary for the performance or has with the consent of the obligee designated a thing to be performed, such thing shall thenceforth constitute the subject matter of the claim.