new-object PSObject causa erro de expressão com valor nulo - powershell, null, expression

Meu script do PowerShell:

Param([string]$Computers) #Must supply a comma seperated list of servers
$Threshold = 20 #Only show CPU over this number
$NoP = 20 #Number of processes to list
$NoRS = 4 #Number of result sets
If (! $Computers) {
Write-Host "Connection to server failed - please specify a server name." -ForegroundColor Red
Break
} Else {
$ComputerList = $Computers -Split " "#,[StringSplitOptions]"RemoveEmptyEntries")
}
$Credential = $host.ui.PromptForCredential("Need credentials", "Please enter your user name and password.", "", "NetBiosUserName")
If (! $Credential) {
Write-Host "Authentication failed - please verify your username and password." -ForegroundColor Red
Break
}
$UserName = $Credential.Username
$Password = $Credential.GetNetworkCredential().Password
$CurrentDomain = "LDAP://" + ([ADSI]"").distinguishedName
$Domain = New-Object System.DirectoryServices.DirectoryEntry($CurrentDomain,$UserName,$Password)
If ($Domain.Name -eq $null){
Write-Host "Authentication failed - please verify your username and password." -ForegroundColor Red
Break
}
ForEach ($ComputerName In $ComputerList) {
$LoadPercentage = $Processors.LoadPercentage
If (!$LoadPercentage) {$LoadPercentage = 0}
Write-Host "Server: $ComputerName (CPU load $LoadPercentage%)" -NoNewline
$Processors = Get-WmiObject win32_processor -ComputerName $ComputerName -Credential $Credential
$i = 1
$TopProcess = @()
$PercentComplete = 0
Do{
$PercentComplete = [Math]::Floor($i/$NoRS*100)
Write-Progress -Activity $ComputerName -Status "$PercentComplete% Complete:" -PercentComplete $PercentComplete
$ProcessList = gwmi Win32_PerfFormattedData_PerfProc_Process -ComputerName $ComputerName -Credential $Credential |
Select IDProcess,Name,PercentProcessorTime |
Where {$_.Name -ne "_Total" -and $_.Name -ne "Idle"} |
Sort PercentProcessorTime -Descending |
Select -First $NoP
ForEach ($Process In $ProcessList) {
$row = New-Object PSObject -Property @{
Id = $Process.IDProcess
Name = $Process.Name
User = (gwmi Win32_Process -ComputerName $ComputerName -Credential $Credential | Where {$_.ProcessId -eq $Process.IDProcess}).GetOwner().User
CPU = $Process.PercentProcessorTime/$Processors.NumberOfLogicalProcessors -f {P}
Description = (gwmi Win32_Process -ComputerName $ComputerName -Credential $Credential | Where {$_.ProcessId -eq $Process.IDProcess}).Description
}
$TopProcess += $row
}
$i++
} While ($i -lt $NoRS + 1)
Write-Progress -Activity $ComputerName -Completed
$Group = $TopProcess | Where {$_.CPU -gt $Threshold} | Group "ID" | Where Count -eq $NoRS
If (!$Group) {
Write-Host " has no processes persistently above $Threshold percent CPU usage."
} Else {
$Processes = @()
ForEach ($Groupee In $Group) {
$Ungroup = $Groupee | Select -ExpandProperty Group
$CPU = 0
ForEach ($ugr in $Ungroup) {
$CPU += $ugr.CPU
}
$row = new-object PSObject -Property @{
Id = $Ungroup.Id | Select -First 1
Name = $Ungroup.Name | Select -First 1
CPU = $CPU/$NoRS
User = $Ungroup.User | Select -First 1
Description = $Ungroup.Description | Select -First 1
}
$Processes += $row
}
$Processes | Format-Table @{Expression={$_.User};Label="User Name";width=25},@{Expression={$_.CPU};Label="CPU";width=5},@{Expression={$_.Id};Label="ID";width=8},@{Expression={$_.Description};Label="Description";width=48}
}
}

intermitentemente dá o seguinte erro:

Você não pode chamar um método em uma expressão de valor nulo. Em C: UsersJasons1CPUusage.ps1: 41 char: 4

• $ row = novo objeto PSObject -Property @ {

• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  • CategoryInfo: InvalidOperation: (:) [], RuntimeException
  • FullyQualifiedErrorId: InvokeMethodOnNull

que não consigo entender como está dentro de um loop e deve funcionar ou ser ignorado, pois há um teste para null.

Respostas:

Certeza de que seus problemas estão decorrentes desta linha:

User = (gwmi Win32_Process -ComputerName $ComputerName -Credential $Credential | Where {$_.ProcessId -eq $Process.IDProcess}).GetOwner().User

Especificamente de .GetOwner(). Sua cláusula where não deve estar encontrando um processo de correspondência para esse item enquanto ele estiver no loop. Sei que não há muito tempo decorrido, mas as consultas WMI não são as coisas mais rápidas por aí.

O que está acontecendo é provavelmente o resultado de um processo consultado anteriormente $ProcessList = gwmi Win32_PerfFormattedData_PerfProc_Process e depois quando você estiver usando gwmi Win32_Process a lista de processos mudou. Você precisa dar conta disso também. O tempo passou e os threads não duram para sempre.

$queryResult = gwmi Win32_Process -ComputerName $ComputerName -Credential $Credential | Where {$_.ProcessId -eq $Process.IDProcess}
$owner = if($queryResult){$queryResult.GetOwner().User}else{"Process DNE"}
#...

User = $owner

Não é muito bonito, mas explica o potencial de um retorno nulo da consulta wmi.