powershell 脚本请帮助 - “您不能在空值表达式上调用方法。”

Question

Here is the script for reference - it is failing at the below line and I'm not sure why - appreciate any help:)

You cannot call a method on a null-valued expression.
At C:\users\jk\documents\jk.ps1:19 char:45
 ... -VMhost | %{$_.ExtensionData.UpdateProductLockerLocation($datastore)} ...                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

script :

Set-PowerCLIConfiguration -InvalidCertificateAction Ignore -Confirm:$false
# VMware VirtualCenter server name 
$VCserver = Read-Host "Enter the vCenter server name"

# Connect to the vCenter server 
Connect-VIServer -server $VCserver

# variable
$cluster = 'cluster01'
$hosts = Get-Cluster -Name $cluster | Get-VMHost
$datastore = '/vmfs/volumes/04c62043-2d22f726/vmwtools/VMware Tools 12.0.6/'

# Display the current VMware Tools location
# default is: /locker/packages/vmtoolsRepo/
$hosts | Get-AdvancedSetting -Name "UserVars.ProductLockerLocation" | Select-Object Entity, Value

# Change the VMware Tools location
Get-cluster -name $cluster | Get-VMhost | %{$_.ExtensionData.UpdateProductLockerLocation($datastore)}  

# Display current VMware Location
$hosts | Get-AdvancedSetting -Name "UserVars.ProductLockerLocation" | Select-Object Entity,Value

# Disconnect from vCenter 
Disconnect-VIserver -server * -Confirm:$false

Answer 1

As the wording of the error message suggests ("You cannot call a method on a null-valued expression."), you tried to call a method on an expression that is effectively $null , which in your case is $_.ExtensionData .

If that expression is expected to be situationally $null in your ForEach-Object ( % ) call, you can simply avoid calling the method whenever you find the expression value to be $null :

In PowerShell (Core) 7.1 and above , you can use the null-conditional operator , ?. :

# PS v7.1+
# Note the use of ?. instead of .
Get-cluster -name $cluster | Get-VMhost |
  ForEach-Object { $_.ExtensionData?.UpdateProductLockerLocation($datastore) } 

As a general caveat :

• While ?. works as expected with properties , with variables it unfortunately and unexpectedly requires the variable name to be enclosed in {...} , because - surprisingly - ? is a legal character in a variable name.
• For instance, Set-StrictMode -Version 2; $foo = $null; ${foo}?.ToUpper() Set-StrictMode -Version 2; $foo = $null; ${foo}?.ToUpper() Set-StrictMode -Version 2; $foo = $null; ${foo}?.ToUpper() works, but using $foo?.ToUpper() instead does not , because PowerShell looks for a variable named $foo? (sic), which doesn't exist. Requesting that this counterintuitive behavior be changed - even though it is technically a breaking change - is the subject of GitHub issue #14025 .

---

In Windows PowerShell you can use an if statement:

Get-cluster -name $cluster | Get-VMhost |
  ForEach-Object { 
    if ($null -ne $_.ExtensionData)  { 
      $_.ExtensionData.UpdateProductLockerLocation($datastore) 
    } 
  }

Note how $null is placed on the LHS (left-hand side) of the -ne operation above (applies equally to -eq ), which is a good habit to form, because it is the only fully reliable way to test for $null - see the docs .