Remove unnecessarily misleading clauses w.r.t. environment variable emptiness (#10850)

[brucificus]

PR Summary

This adjusts some wording to not inappropriately state that environment variables cannot be empty strings when they can be empty strings.

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[brucificus]

@microsoft-github-policy-service agree

[github-actions]

Expectations

Thanks for your submission! Here's a quick note to provide you with some context for what to expect from the docs team and the process now that you've submitted a PR. Even if you've contributed to this repo before, we strongly suggest reading this information; it might have changed since you last read it.

To see our process for reviewing PRs, please read our editor's checklist and process for managing pull requests in particular. Below is a brief, high-level summary of what to expect, but our contributor guide has expanded details.

The docs team begins to review your PR if you request them to or if your PR meets these conditions:

• It is not a draft PR.
• It does not have a WIP prefix in the title.
• It passes validation and build steps.
• It does not have any merge conflicts.
• You have checked every box in the PR Checklist, indicating you have completed all required steps and marked your PR as Ready to Merge.

You can always request a review at any stage in your authoring process, the docs team is here to help! You do not need to submit a fully polished and finished draft; the docs team can help you get content ready for merge.

While reviewing your PR, the docs team may make suggestions, write comments, and ask questions. When all requirements are satisfied, the docs team marks your PR as Approved and merges it. Once your PR is merged, it is included the next time the documentation is published. For this project, the documentation is published daily at 3 p.m. Pacific Standard Time (PST).

[sdwheeler]

@brucificus Thanks for the contribution. However, the documentation is correct as written. If you set an environment variable to an empty string, that variable is removed. For example:

# TESTVAR does not exist
PS> dir Env:TESTVAR
Get-ChildItem: Cannot find path 'TESTVAR' because it does not exist.
# Create TESTVAR
PS❯ $Env:TESTVAR = 123
PS> dir Env:TESTVAR

Name                           Value
----                           -----
TESTVAR                        123

# Set it to $null and see that it no longer exists
PS❯ $Env:TESTVAR = $null
PS> dir Env:TESTVAR
Get-ChildItem: Cannot find path 'TESTVAR' because it does not exist.
PS❯ $Env:TESTVAR = ''
PS> dir Env:TESTVAR
Get-ChildItem: Cannot find path 'TESTVAR' because it does not exist.

[learn-build-service-prod]

Learn Build status updates of commit 0a32fce:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/5.1/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-5.1)
reference/7.2/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.2)
reference/7.3/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.3)
reference/7.4/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.4)
reference/7.5/Microsoft.PowerShell.Core/About/about_Environment_Variables.md	✅Succeeded	View (powershell-7.5)

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel