(#310) Fix issue with environment handling

[vexx32]

Description Of Changes

• Only return environment variable names that have an associated value from Get-EnvironmentVariableNames
• When calling Update-SessionEnvironment, don't call SetVariable if the value at the queried scope is null.

Motivation and Context

• .NET's registry handling seems to get value names around that have been set to null previously in the session, causing issues with the UpdateSession logic path.

Testing

Testing in test kitchen where we noticed the issue.

Operating Systems Testing

Windows Server 2016 & 2019

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v2 compatibility checked?

Related Issue

#310

[gep13]

@vexx32 @corbob am I right in saying that this PR is no longer required?

If so, let's go ahead and close it out.

[gep13]

As discussed in a Zoom call, this PR is no longer required.