redef fun is_nullable: Bool do return true
redef fun <(t) do return t isa MMTypeNone or t isa MMNullableType
redef fun to_s do return "null"
redef fun is_nullable: Bool do return true
redef fun <(t) do return t isa MMTypeNone or t isa MMNullableType
redef fun to_s do return "null"