New-Guid -Empty ignores an explicit $false value

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This is one of many instances of a shipped command that doesn't behave correctly when a switch parameter is explicitly passed a $false value.

For context, see:

Fix individual commands that do not respect an explicit $false value passed to a switch parameter #25242

Steps to reproduce

New-Guid -Empty:$false

# Equivalent, with hash table splatting:
$params = @{ Empty = $false }
New-Guid @params

Expected behavior

New-Guid emits a non-empty [guid] instance. For example:

Guid
----
d2a83da7-6092-4c06-b8de-3b9aadbd8c94

Actual behavior

The $false value is ignored and an empty [guid] instance is emitted.

Guid
----
00000000-0000-0000-0000-000000000000

New-Guid uses the selected parameter set name (Empty), which is based on the presence of the switch parameter (not its value), to determine the behavior.

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/NewGuidCommand.cs

Line 52 in f194359

guid = ParameterSetName is "Empty" ? Guid.Empty : Guid.NewGuid();

Behavior should be determined by the value of the Empty property instead.

Environment data

Name                           Value
----                           -----
PSVersion                      7.6.0-preview.3
PSEdition                      Core
GitCommitId                    7.6.0-preview.3
OS                             Microsoft Windows 10.0.19045
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0, 5.0, 5.1…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

There will , no doubt, be someone who says "well don't set switches to false then"
However if you have

function mine { 
Param {[switch]$mySwitch}

some-cmdlet -SomeSwitch:MySwitch 
}

You rely on switches behaving properly with false.
There are plenty of bugs in the world where "present" and "evaluates to true" are wrongly assumed to be the same (e.g. if ($color) {set-color $color} where color is an enum and 0=Black. So if black is requested the code doesn't run. Using a parameter set to infer parameter values is a new variation , but shouldn't be in a cmdlet.

There may be other unnoticed ones

However if you have

I tried and it does not work. The term 'Param' is not recognized..., Cannot convert 'System.String' to the type 'System.Management.Automation.SwitchParameter' required by parameter 'Empty'

237dmitry

237dmitry: That is just a typo: it should be Param (...), not Param { ... }

For the backstory, see:

Treat -Switch:$false the same as omitting a switch when selecting a parameter set #25027

Since said proposal was rejected, the affected cmdlets must now be fixed one by one (these cmdlets were identified by surfingoldelephant in #25242).

Perhaps needless to say, not fixing the counterintuitive behavior in general will continue to trip up cmdlet authors, both third-party and Microsoft-internal ones.

it should be Param (...), not Param { ... }

This is not working too:

& {
  function mine { 
      Param ( [switch]$mySwitch )
     new-guid -empty:$mySwitch 
  }
  
  mine -mySwitch   # mine # mine -mySwitch # -mySwitch:$true or $false    
  }

237dmitry

237dmitry, your example is working (with mine -mySwitch you're asking for an empty GUID and you're getting one), while mine (which makes $mySwitch implicitly $false in a Boolean context such as -empty:$mySwitch) and mine -mySwitch:$false aren't (you're still getting an empty GUID, despite negating the -Empty switch), which is what this issue is about.

you're asking for an empty GUID and you're getting one

No, although I don't like such a syntactic technique as explicit use of boolean values in switch variables, it looks, frankly, ugly, I just tried to see if it would work with passing another switch. It turned out that it doesn't work. The result is exactly the same as in the essence of the issue itself.

I check if it was like $true -and $false

Cmdlet WG reviewed this. We agree this is a bug. This should not be a difficult fix.

Added test of New-Guid -Empty:$false to New-Guid.Tests.ps1, reproduci…

surfingoldelephant

📣 Hey @surfingoldelephant, how did we do? We would love to hear your feedback with the link below! 🗣️

🔗 https://aka.ms/PSRepoFeedback

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`New-Guid -Empty` ignores an explicit `$false` value #25276

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New-Guid -Empty ignores an explicit $false value #25276

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jhoneill commented on Apr 4, 2025

237dmitry commented on Apr 4, 2025

mklement0 commented on Apr 4, 2025

237dmitry commented on Apr 4, 2025

mklement0 commented on Apr 4, 2025

237dmitry commented on Apr 4, 2025

TobiasPSP commented on May 7, 2025

microsoft-github-policy-service commented on Oct 6, 2025

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`New-Guid -Empty` ignores an explicit `$false` value #25276