400.2-202.  Final written expression — parol or extrinsic evidence. — Terms with respect to which the confirmatory memoranda of the parties agree or which are otherwise set forth in a writing intended by the parties as a final expression of their agreement with respect to such terms as are included therein may not be contradicted by evidence of any prior agreement or of a contemporaneous oral agreement but may be explained or supplemented

  (a)  by course of dealing or usage of trade (section 400.1-205) or by course of performance (section 400.2-208); and

  (b)  by evidence of consistent additional terms unless the court finds the writing to have been intended also as a complete and exclusive statement of the terms of the agreement.