Section 1--103. Supplementary General Principles of Law Applicable.
    Unless  displaced  by  the  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 cause shall supplement its provisions.