Bug: config-based `SkipGlob` and `TargetGlob` get overwritten when not specified on CLI

[Aaronontheweb]

Reproduction spec here:

/*
     *  Looking for a suspected bug where:
     * 
     *  1. No globs specified on command line
     *  2. globs specified in config file
     *  3. Parse operation supplies an empty array instead of a null array
     *  4. Merge operation fails because it uses the empty array instead of the config file globs
     */
    [Fact]
    public void ShouldKeepConfigGlobs()
    {
        string[] expectedGlobs = ["**/*.Tests.csproj", "**/tests/*.csproj"];
        var args = CommandLineParser
            .SplitCommandLineIntoArguments("run", true).ToArray();
        var r = TryParseSlnOptions(args, out SlnOptions? result);

        Assert.Equal(0, r);
        Assert.NotNull(result);
        
        var config = new IncrementalistConfig
        {
            TargetGlob = null,
            SkipGlob = expectedGlobs,
            GitBranch = "dev",
            WorkingDirectory = @"C:\user\workingdir"
        };
        
        var merged = ConfigMerger.Merge(result, config);
        Assert.Equivalent(expectedGlobs, merged.SkipGlobs);
    }

[Aaronontheweb]

The issue here is the CLI parser is supply an empty array instead of a null one, and we're not checking for that upon config merge.