Modification under the UCC
UCC 2-209(1) - "An agreement modifying a contract within this Article [Art. 2] needs no consideration to be binding”
UCC 1-304- "Every contract or duty within [the Uniform Commercial Code] imposes an obligation of good faith in its performance"-
UCC does not have a pre-exisiting duty rule, policy concerns satisfied by UCC 2-209 and 1-304 together.