How to enforce required command-line options with NDesk.Options?

I was just writing a console utility and decided to use NDesk.Options for command-line parsing. My question is, How do I enforce required command-line options?

I see in the docs that:

options with a required value (append '=' to the option name) or an optional value (append ':' to the option name).

However, when I put a = at the end of the option name there is no difference in behavior. Ideally the Parse method would throw an exception.

Is there something else I need to do?

Here is my test code:

class Program
{
    static void Main(string[] args)
    {
        bool show_help = false;
        string someoption = null;

        var p = new OptionSet() {
            { "someoption=", "Some String Option", v => someoption = v},
            { "h|help",  "show this message and exit", v => show_help = v != null }
        };

        List<string> extra;
        try
        {
            extra = p.Parse(args);
        }
        catch (OptionException e)
        {
            System.Console.Write("myconsole: ");
            System.Console.WriteLine(e.Message);
            System.Console.WriteLine("Try `myconsole --help' for more information.");
            return;
        }

        if (show_help)
        {
            ShowHelp(p);
            return;
        }

        System.Console.WriteLine("==================");
        System.Console.WriteLine(someoption);
    }

    static void ShowHelp(OptionSet p)
    {
        System.Console.WriteLine("Usage: myconsole [OPTIONS]");
        System.Console.WriteLine();
        System.Console.WriteLine("Options:");
        p.WriteOptionDescriptions(System.Console.Out);
    }
}