∀ {α : Type u} {β : Type v} {m : Std.HashMap.Raw α β} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α]
  [LawfulHashable α] [inst_4 : Inhabited β], m.WF → ∀ {a : α}, m.contains a = false → m[a]! = default