Empty value in runsettings should be treated as the tag not being present at all unless overridden

[nohwnd]

Description

Make providing provide empty value in runconfiguration the same as not specifying the tag at all, unless the option forces it. Currently not providing TargetFrameworkVersion fails the run, while omitting the tag falls to auto-detection. Which is our desired approach anyway. There are probably many options like this. And it makes authoring runsettings painful.

<RunSettings>
<RunConfiguration>
    <TargetFrameworkVersion></TargetFrameworkVersion>    
</RunConfiguration >
</RunSettings>

C:\> dotnet test --diag:logs2\log.txt --settings .\r.runsettings

...

Microsoft (R) Test Execution Command Line Tool Version 17.2.0-preview-20220207-08
Copyright (c) Microsoft Corporation.  All rights reserved.

Settings file provided does not conform to required format. An error occurred while loading the settings.  
Error: Invalid setting 'RunConfiguration'. Invalid value '' specified for 'TargetFrameworkVersion'..

Steps to reproduce

Don't provide value to tfm and it fails.

Expected behavior

I would expect to just fallback to auto-detection, as if the tag is not specified at all.

Actual behavior

It fails my run.

Diagnostic logs

Environment

AB#1865121

[nohwnd]

Seems like a simple thing worth a look. Or closing if it is too complicated because there are no more asks for this.