Is it possible to have [Nullable[bool]] in a bool[] in PowerShell - powershell

Question

Is it possible to have [Nullable[bool]] in a bool[] in PowerShell? I tried different solution, approaches but fail to get proper $null, $true, $false for a parameter? Also it seems that [cmdletbinding] changes how things works as well.
enum BoolNull {
null = $null
true = $true
false = $false
}
function Test-Array0 {
param (
[bool[]] $thisValue
)
if ($thisValue -eq $null) {
Write-Output 'Null found'
}
}
function Test-Array1 {
param (
[bool[]] $thisValue
)
foreach ($value in $thisValue) {
if ($value -eq $null) {
Write-Output 'Null found'
}
}
}
function Test-Array2 {
[CmdletBinding()]
param (
[bool[]] $thisValue
)
if ($thisValue -eq $null) {
Write-Output 'Null found'
}
}
function Test-Array {
[CmdletBinding()]
param (
[AllowEmptyCollection()] [AllowNull()][ValidateSet($null, $true, $false)] $thisValue
)
if ($thisValue -eq $null) {
Write-Output 'Null found'
}
}
# this works
function Test-Test {
[CmdletBinding()]
param (
[nullable[bool]] $thisValue
)
if ($thisValue -eq $null) {
Write-Output 'Null found'
}
}
function Test-Array5 {
param (
[boolnull[]] $thisValue
)
foreach ($value in $thisValue) {
if ($value -eq 'null') {
Write-Output 'Null found'
}
}
}
Test-Array0 -thisValue $null #this works
Test-Array -thisValue $null # this doesn't work
Test-Array -thisValue $null, $null, $true # this doesn't work
Test-Array1 -thisValue $null
Test-Array2 -thisValue $null # this
Test-Test -thisValue $null # this works
Test-Array5 -thisValue null, true, null # this works but is completely useless

Answer 1

This is a limitation of the bool type. When you strictly-type the parameter, it can only take $true, $false, 0, and 1. In order to achieve what you want, you can use a [ValidateSet] attribute:
[CmdletBinding()]
param(
[Parameter(Position = 0, Mandatory)]
[ValidateSet($null, $true, $false)]
[object] $ThisValue
)
As a side-note, there used to be a bug with powershell (might still be present) where comparing $null on the right side will cause nothing to be returned, causing logic to fall out of the statement, so it's best to compare on the left:
if ($null -eq $ThisValue) {
After testing your example, I was unable to replicate your problem, however:
function Test-Nullable {
[CmdletBinding()]
param(
[nullable[bool]] $Value
)
if ($null -eq $Value) {
'Yes'
} else {
$Value
}
}
and in array format:
function Test-Nullable {
[CmdletBinding()]
param(
[nullable[bool][]] $Value
)
foreach ($bool in $Value) {
if ($null -eq $bool) {
'Yes'
} else {
$bool
}
}
}
Test-Nullable 5, 3, $null, $true, $false, 0
True
True
Yes
True
False
False