PsCustomObject - controlling null or not null value

My workflow is :

• if manager field is not null , I will add this value inside pscustomobject.

• if manager field is NULL , I will add NULL keyword.

This line is not working correctly.

manager = if ((Get-ADuser -identity $obj.Manager)) {'(Get-ADuser -identity $obj.Manager -properties displayname).DisplayName'} Else {'NULL'}

script :

$Objects = Get-ADUser -identity user01 -properties *

foreach ($obj in $Objects) {
   
    $LogonDate = (Get-LastLogon -Identity $obj.SamAccountName).DateTime
    $logging += [PSCustomObject]@{
        DisplayName = $obj.Name
        samaccountname = $obj.samaccountname
        mail = $obj.mail
        title = $obj.title
        department = $obj.department
        manager = if ((Get-ADuser -identity $obj.Manager)) {(Get-ADuser -identity $obj.Manager -properties displayname).DisplayName} Else {$null}
        physicalDeliveryOfficeName = $obj.physicalDeliveryOfficeName
        postalCode = $obj.postalCode
        State = $obj.St
        description = $obj.description
        Country = $obj.c
        company =$obj.company
        homephone = $obj.homephone
        telephoneNumber = $obj.telephoneNumber
        mobile = $obj.mobile
        Location = $obj.l
        LastLogon   = $LogonDate
    }
}

$logging

Error Message:

Get-ADUser : Cannot validate argument on parameter 'Identity'. The argument is null. Provide a valid value for the argument, and then try running the command again.
At line:18 char:45
+         manager = if ((Get-ADuser -identity $obj.Manager)) {(Get-ADus ...
+                                             ~~~~~~~~~~~~
	+ CategoryInfo          : InvalidData: (:) [Get-ADUser], ParameterBindingValidationException
	+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.ActiveDirectory.Management.Commands.GetADUser

As top line inside the foreach loop do

$manager = if (![string]::IsNullOrWhiteSpace($obj.Manager)) {
                (Get-ADUser -Identity $obj.Manager -Properties DisplayName).DisplayName
           } else {'NULL'}

then in your [PsCustomObject] you set manager = $manager

or do something like

$manager = Get-ADUser -Identity $obj.Manager -Properties DisplayName -ErrorAction SilentlyContinue

then in your [PsCustomObject] you set manager = if ($manager) { $manager.DisplayName } else { 'NULL'}

BTW, you should not use += to add objects to an array (which you didn't declare on top of the script..)

Instead use

$logging = foreach ($obj in $Objects) { ... }

Also, using -Properties * is very wasteful because you then ask for ALL user properties where you only want a subset.
In this case I would create an array of properties to fetch on top

$props = 'DisplayName', 'EmailAddress', 'Title', 'Department', 'Manager', 'Office', 'PostalCode', 
         'State', 'Description', 'Country', 'Company', 'HomePhone', 'OfficePhone', 'MobilePhone', 'City'
$Objects = Get-ADUser -Filter * -Properties $props

P.S. I'm using PowerShell aliases here but you can use the LDAP attribute names if you like that better:

Why do it that way at all - you're reconstructing an object for no reason?

Get-ADUser -identity gordom04 -Properties * | Select-Object Name,
                                                  samaccountname,
                                                  mail,
                                                  title,
                                                  department,
                                                  @{Name='Manager';Expression={(Get-AdUser $_.Manager -Properties DisplayName).DisplayName}},
                                                  physicalDeliveryOfficeName,
                                                  postalCode,
                                                  State,
                                                  description,
                                                  Country,
                                                  company,
                                                  homephone,
                                                  telephoneNumber,
                                                  mobile,
                                                  Location,
                                                  @{Name='LastLogon';Expression={[DateTime]::FromFileTime($_.LastLogon)}}

Or, if you have a list of users you need and need it saved to an object:

$Objects = 'user01','user02'

$ResultObj = $Objects | ForEach-Object {
    Get-ADUser -Identity $_ -Properties * | Select-Object Name,
                                                 samaccountname,
                                                 mail,
                                                 title,
                                                 department,
                                                 @{Name='Manager';Expression={(Get-AdUser $_.Manager -Properties DisplayName).DisplayName}},
                                                 physicalDeliveryOfficeName,
                                                 postalCode,
                                                 State,
                                                 description,
                                                 Country,
                                                 company,
                                                 homephone,
                                                 telephoneNumber,
                                                 mobile,
                                                 Location,
                                                 @{Name='LastLogon';Expression={[DateTime]::FromFileTime($_.LastLogon)}}
}
# Output results
$ResultObj