Section 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 performance, course of dealing, or usage of trade
(Section 1--303); 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.