Model Binder for properly handling null values. See this post here for more details: http://juristr.com/blog/2012/02/aspnet-mvc3-doesnt-deserialize-nullable

ModelBinder.cs

public class ModelBinder : IModelBinder
{
    private IModelBinder fallbackModelBinder;

    public ModelBinder(IModelBinder fallbackModelBinder)
    {
        this.fallbackModelBinder = fallbackModelBinder;
    }

    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        if (controllerContext.HttpContext.Request.HttpMethod.Equals("GET", StringComparison.InvariantCultureIgnoreCase)) 
            //|| controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
        {
            return this.fallbackModelBinder.BindModel(controllerContext, bindingContext);
        }
        else
        {
            if (controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
            {
                //ONLY do this for POST,PUT,DELETE requests that transmit application/json
                string bodyText;

                using (var stream = controllerContext.HttpContext.Request.InputStream)
                {
                    stream.Seek(0, SeekOrigin.Begin);
                    using (var reader = new StreamReader(stream))
                        bodyText = reader.ReadToEnd();
                }

                if (string.IsNullOrEmpty(bodyText))
                    return (null);

                return JsonConvert.DeserializeObject(bodyText, bindingContext.ModelType,
                                                     new[] { new IsoDateTimeToLocalTimeConverter() { 
                                                         Culture = new System.Globalization.CultureInfo("de-DE"),
                                                         DateTimeStyles = System.Globalization.DateTimeStyles.AssumeUniversal
                                                     }});
            }
            else
            {
                return this.fallbackModelBinder.BindModel(controllerContext, bindingContext);
            }
        }
    }
}