68 Pa.C.S. § 4108

The principles of law and equity, including the law of corporations and nonprofit corporations and unincorporated associations, the law of real property and the law relative to the capacity to contract, principal and agent, eminent domain, estoppel, fraud, misrepresentation, duress, coercion, mistake, receivership, substantial performance or other validating or invalidating cause supplement the provisions of this subpart, except to the extent inconsistent with this subpart.