F# Enum Style Discriminated Unions serialized to strings with Json.NET for DUs with empty cases

JsonConfig.fs

// Fsharp 4.1.0
open System
open Newtonsoft.Json // 10.0.3
open Newtonsoft.Json.Converters

type ToStringJsonConverter () =
    inherit JsonConverter()
    override this.CanConvert objectType = true;

    override this.WriteJson (writer: JsonWriter, value: obj, serializer: JsonSerializer): unit = 
        writer.WriteValue(value.ToString())

    override this.CanRead = false

    override this.ReadJson (reader: JsonReader, objectType: Type, existingValue: obj, serializer: JsonSerializer) : obj =
        raise (new NotImplementedException());


do
    let settings = new JsonSerializerSettings()
    settings.Converters.Add(new StringEnumConverter (CamelCaseText = true))
    JsonConvert.DefaultSettings <- fun () -> settings

[<JsonConverter(typeof<ToStringJsonConverter>)>]
type HowLame =
| PrettyLame
| SuperLame

type LameScale = 
| One = 1
| Ten = 10

type Lame = {
    howLame: HowLame;
    onAScaleOf: LameScale;
}

[<EntryPoint>]
let main argv =
    let lame = { howLame = PrettyLame;
                 onAScaleOf = LameScale.Ten }
    let ser = JsonConvert.SerializeObject(lame)

    // {"soLame":{"Case":"PrettyLame"}} by default
    printfn "%s" ser

    0 // return an integer exit code