Suppose that Ciera rear-ends Dianne’s car while Dianne is sitting at a stop light. Dianne claims that her injuries resulting from her accident are substantial, and she demands that Ciera pay her $50,000. Ciera initially offers merely to pay Dianne’s medical expenses ($9,760), but she eventually offers to pay $25,000 in return for Dianne’s execution of a settlement agreement. As part of the settlement agreement, Dianne must promise not to sue Ciera for her injuries. If the parties consent to the settlement agreement, Dianne’s promise not to sue is what type of consideration?