``` [Option('b', "BookIds", Required = false, HelpText = "List of Books", Separator = ',')] public IEnumerable<string> Bookids { get; set; } [Option('v', "Verbose", Required = false, Hidden = true, HelpText = "Generate Book details", Default = "Yes")] public string All { get; set; } ``` ProcessBooks -b -v NO ------------ If option has separator attribute and when empty value provided... fails; it considers other argument as its values.. In this case; -b has value -v and NO;