An arbitration provision in a payday loan agreement was held unenforceable because the provision’s exclusive designated arbitrator, the Cheyenne River Sioux Tribal Nation, was unavailable and no substitute could be appointed. Parm v. Nat’l Bank of Cal., N.A., 2016 WL 4501661 (11th Cir. Aug. 29, 2016) (Dubina, J.). The lender, Western Sky Financial, conceded that…