unable to set default value using Uri

trying to be able to run an app like this:
consoleApp.exe
or
consoleApp.exe http://someOtherUri.invalid:1234

i can get the default value to work using a string:
class Options{
[Value(0,
Default = "http://someUri.invalid:1234"
)]
public string OptionalUri { get;set;}
}

but not using a Uri as its type.
class Options{
[Value(0,
Default = "http://someUri.invalid:1234"
)]
public Uri OptionalUri { get;set;}
}

static void Main(string[] args)
{
CommandLine.Parser.Default.ParseArguments(args)
.WithParsed(Run)
.WithNotParsed(HandleParseError);
}
static void Run(Options options)
{
//Uri u = options.OptionalUri;
Uri u = new Uri(options.OptionalUri); // possible parseerrors, should've been handled in commandlineparser
}

then i get
Error setting value to option '': Check if Option or Value attribute values
are set properly for the given type.