WebApiConfig.cs

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();
        config.Configure(c =>
        {
            c.CamelCaseSerialization = true;
            c.RemoveXmlFormatter = true;
        });
        
        /* Keep all null values for React and checkout component state handling */
        config.Formatters.JsonFormatter.SerializerSettings = new JsonSerializerSettings
        {
            NullValueHandling = NullValueHandling.Include,
            ContractResolver = new CamelCasePropertyNamesContractResolver()
        };

        config.Formatters.JsonFormatter.UseDataContractJsonSerializer = false;
    }
}

WebApiInitialization.cs

[InitializableModule]
[ModuleDependency(typeof(FrameworkInitialization))]
public class WebApiInitialization : IInitializableModule
{
    public void Initialize(InitializationEngine context)
    {
        WebApiConfig.Register(GlobalConfiguration.Configuration);
    }

    public void Uninitialize(InitializationEngine context)
    {
    }
}