The provisions on fraud, threat, gross disparity and illegality contained in this Chapter are mandatory.
The provisions of this Chapter relating to fraud, threat, gross disparity and illegality are of a mandatory character. It would be contrary to good faith for the parties to exclude or modify these provisions when concluding their contract. However, nothing prevents the party entitled to avoidance for fraud, threat and gross disparity to waive that right once that party learns of the true facts or is able to act freely.
On the other hand, the provisions of this Chapter relating to the binding force of a mere agreement, to initial impossibility or to mistake are not mandatory. Thus the parties may reintroduce special requirements of domestic law, such as consideration or cause. They may likewise agree that their contract shall be invalid in case of initial impossibility, or that mistake by one of the parties is not a ground for avoidance.