Test-Path: Update documentation

[vexx32]

Issue Details

Ref: PowerShell/PowerShell#8080

Test-Path is being altered to accept null/empty string input. I believe the behaviour will be as follows:

• For $null input: write non-terminating error to error stream
• For empty string '' input: return $false

Version(s) of document impacted

• Impacts 6.next document
• Impacts 6 document
• Impacts 5.1 document
• Impacts 5.0 document
• Impacts 4.0 document
• Impacts 3.0 document

Reason(s) for not selecting all version of documents

• The documented feature was introduced in selected version of PowerShell
• This issue only shows up in selected version of the document

[SteveL-MSFT]

Fixed by #4036