YsodStatusCodeHandler.cs

public class YsodStatusCodeHandler : IStatusCodeHandler
{
    public bool HandlesStatusCode(HttpStatusCode statusCode, NancyContext context)
    {
        return statusCode == HttpStatusCode.InternalServerError;
    }

    public void Handle(HttpStatusCode statusCode, NancyContext context)
    {
        object error;
        if (context.Items.TryGetValue(NancyEngine.ERROR_EXCEPTION, out error))
        {
            var exception = error as Exception;
            if (exception != null)
            {
                throw exception;
            }
        }
    }
}