Cecilia is a hair stylist. A customer threatened to sue Cecilia because her hair turned green after Cecilia worked on it. Cecilia knew that the customer's hair was damaged, but that she told the customer that odd results could result from any dye attempt and had her sign a contract that she released Cecilia from all liability and would not sue. The customer sued anyway. What type of agreement did Cecilia have the customer with green hair sign?