The provisions of this article relating to the legal capacity of a conservatee to bind or obligate the conservatorship estate, and the provisions of any order of the court broadening such capacity, do not displace but are supplemented by general principles of law and equity relating to transactions including, but not limited to, capacity to contract, joinder or consent requirements, estoppel, fraud, misrepresentation, duress, coercion, mistake, or other validating or invalidating cause.