Nullable boolean Options aren't supported

[goncalo-oliveira]

Describe the bug

When using a nullable boolean with an option of type CommandOptionType.SingleOrNoValue, the argument value isn't binded. It only works if the property isn't nullable.

To Reproduce

Using version 4.0.2 of the library. To reproduce, add a property with a nullable boolean

public class InstallCommand
{
    [Option( "--install-proxy", CommandOptionType.SingleOrNoValue )]
    public bool? InstallProxy { get; set; }

    protected Task<int> OnExecute( CommandLineApplication app )
    {
        Console.WriteLine( $"install proxy: {InstallProxy}" );

        return Task.FromResult( 0 );
    }
}

Execute with the argument --install-proxy or --install-proxy=true or --install-proxy=false.

The InstallProperty value will still be set to null.

The output

$ dotnet run -- install --install-proxy
install proxy: 

Expected behavior

I would expect the argument value to be binded to the property value.

Screenshots

[natemcmaster]

Did you try this instead?

CommandLineUtils/docs/docs/options.md

Lines 73 to 76 in 81199c7

	[Option]
	public (bool hasValue, string value) LogLevel { get; set; }
	// Inferred type = SingleOrNoValue
	// Inferred names = "-l", "--log-level"