Internal Server Error

Prelude.maximum: empty list
CallStack (from HasCallStack):
  error, called at libraries/base/GHC/List.hs:1646:3 in base:GHC.List
  errorEmptyList, called at libraries/base/GHC/List.hs:717:28 in base:GHC.List
  maximum, called at libraries/base/Data/Foldable.hs:745:15 in base:Data.Foldable