PowerShell - Adding New User to Selection of AD Groups - powershell

Question

I've created a form to create new AD Accounts. Part of the script determines which groups the new user will be added to based on their role (Doctor, Nurse, Admin or Other) which is captured in the following code in the form of a drop down pick box:
Write-Host "Based on this information" $FFN "has been added to the following Active Directory Groups:"
Write-Host
$ADGroup01 = Get-ADGroup "_XA_App_XenApp" |select -expandproperty name -first 1
Write-Host $ADGroup01
$ADGroup02 = Get-ADGroup "Web Proxy Users" |select -expandproperty name -first 1
Write-Host $ADGroup02
if($RadioButton1.Checked -eq $true)
{
$ADGroup03 = Get-ADGroup "allrot" |select -expandproperty name -first 1
Write-Host $ADGroup03
}
Else
{
$ADGroup03 = Get-ADGroup "alltpo" |select -expandproperty name -first 1
Write-Host $ADGroup03
}
if ($Role -eq "Doctor" -Or $Role -eq "Nurse")
{
$ADGroup04 = Get-ADGroup "PACS Web Access" |select -expandproperty name -first 1
Write-Host $ADGroup04
}
if ($Role -eq "Doctor")
{
$ADGroup05 = Get-ADGroup "CH-MFD" |select -expandproperty name -first 1
Write-Host $ADGroup05
$ADGroup06 = Get-ADGroup "ED-MFP" |select -expandproperty name -first 1
Write-Host $ADGroup06
$ADGroup07 = Get-ADGroup "SU-MFD" |select -expandproperty name -first 1
Write-Host $ADGroup07
}
Write-Host
Further on in the script this piece of code is called during the actual account creation process:
Add-ADPrincipalGroupMembership -Identity $UN -memberof $ADGroup01, $ADGroup02, $ADGroup03, $ADGroup04, $ADGroup05, $ADGroup06, $ADGroup07
The issue I'm facing is that if the user selects Nurse, Admin or Other I get the following error:
"Add-ADPrincipalGroupMembership : Cannot validate argument on parameter 'MemberO
f'. The argument is null, empty, or an element of the argument collection conta
ins a null value. Supply a collection that does not contain any null values and
then try the command again."
I know this is because there are no values being captured in the last $ADGroup[x] and short of creating a bunch of if statements to check if each $ADGroup contains data I'm wondering if there is a more elegant solution.
As always, thank you for taking the time review and happy to provide more information if required.
UPDATE - As per #Martin's advice I've implemented the following code into my script
$UN = "zooz"
$Role = "Nurse"
$Department = "Surgical"
If ($Role -eq "Doctor" -and $Department -eq "Surgical")
{
$ADGroups = #(
"PACS Web Access"
"CH-MFD"
"ED-MFP"
"SU-MFD"
)
}
If ($Role -eq "Nurse" -and $Department -eq "Surgical")
{
$ADGroups = #(
"_XA_App_XenApp"
"Web Proxy Users"
"allrot"
)
}
for ($i=0; $i -lt $ADGroups.length; $i++) {
Add-ADPrincipalGroupMembership -Identity $UN -memberof $adgroups[$i]
}

Answer 1

Make an object $adgroups and add your desired groups to it.
$adgroups = #()
At the end use a foreach Loop:
$adgroups | Add-ADPrincipalGroupMembership -Identity $UN or (weather or not the cmdlet likes pipelined Input)
$adgroups | % { Add-ADPrincipalGroupMembership -Identity $UN -memberof $_ }