Okla. Stat. tit. 12, § 12-729.14
Principles of law and equity - Construction of act
Unless displaced by particular provisions of this act, the
principles of law and equity, including the law merchant, and the
law relative to capacity to contract, principal and agent, estoppel,
fraud, misrepresentation, duress, coercion, mistake, bankruptcy or
other validating or invalidating causes supplement its provisions.