584 F.3d 253, 303 (6th Cir. 2009) ("It is hornbook law that all parties to a contract are necessary in an action challenging its validity . . . ."); Dawavendewa v. Salt River Project Agr. Imp. & Power Dist, 276 F.3d 1150, 1157 (9th Cir. 2002) ("[A] party to a contract is necessary, and if not susceptible to