Option converter for Newtonsoft!
========================

.. code-block:: fsharp
   
     //      Ayrat Hudaygulov, [17.03.19 00:52] https://t.me/fsharp_chat
     /// For Some 1 genereates "1", for None generates "null"
     type OptionConverter() =    
         inherit JsonConverter()
         
         override x.CanConvert(typ) = typ.IsGenericType && typ.GetGenericTypeDefinition() = typedefof<option<_>>
     
         override x.WriteJson(writer, value, serializer) =
             let value = 
                 if isNull value then null
                 else 
                     let _,fields = FSharpValue.GetUnionFields(value, value.GetType())
                     fields.[0]  
             serializer.Serialize(writer, value)
     
         override x.ReadJson(reader, typ, existingValue, serializer) =
             let innerType = 
                 let innerType = typ.GetGenericArguments().[0]
                 if innerType.IsValueType then typedefof<Nullable<_>>.MakeGenericType([|innerType|])
                 else innerType        
             
             let cases = Util.getAndCacheUnionCases typ
             if reader.TokenType = JsonToken.Null then FSharpValue.MakeUnion(cases.[0], Array.empty)
             else
                 let value = serializer.Deserialize(reader, innerType)
                 if isNull value then FSharpValue.MakeUnion(cases.[0], Array.empty)
                 else FSharpValue.MakeUnion(cases.[1], [|value|])
     
      ///......
     let s = new JsonSerializer()    
     s.Converters.Add(new OptionConverter())
     
     s.Serialize(someObject)