A mistake of law constitutes a mistake within the meaning of this
Article only when it arises from —

1. A misapprehension of the law by all parties, all supposing that they knew and understood it, and all making substantially the same mistake as to the law; or

2. A misapprehension of the law by one party, of which the others are aware at the time of the contracting, but which they do not rectify.

SOURCE: CC § 1578.