Switch fails with null value

Steps to reproduce

$var = get-process | out-null
switch ($var) {
  $null { write-host NULL }
  default { write-host DEFAULT }
}

In my specific case, I assign $var to the output of a native command that, in some expected cases, doesn’t return anything. Note that explicitly assigning $var = $ null appears to be not the same thing and doesn’t trigger the issue.

Expected behavior

Expecting the switch to be evaluated and the $null clause honored.

Actual behavior

The switch is entirely skipped.

Environment data

PSVersion                      6.2.2
PSEdition                      Core
GitCommitId                    6.2.2
OS                             Microsoft Windows 10.0.18362
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[vexx32]

@EPinci the output of a native command cannot result in a true $null assignment, because native commands only deal with text output. You can get “nothing”, you can sometimes in odd cases get an empty string value ( [string]::Empty or '' ), or a string containing just whitespace.

Native commands don’t deal with the CLR, so they don’t have the ability to pass a $null value to another utility like PowerShell.

[SeeminglyScience]

If I get it right… the “AutomationNull” is equal to “unassigned”?

More like “no results”. It acts a bit differently than an unassigned variable in some cases. It’s a bit like how a SQL query could return a literal NULL value or just not find any matching results.

AutomationNull is like a mix between an empty collection (e.g. @() )and $null. A bit closer to an empty collection than $null.