Q:

How to show all value that have a null entry in a specific column

I am wanting to bring forward a CSV file containing all users Name, SamAccountName and Description, however we have noticed that there are several people who do not have descriptions. What I am looking for is how to edit my existing code (I know there's a simple way to do it I just can't remember it) so that is filters my output so it only shows users who have no description.
Get-ADUser -Filter * -Properties Name,SamAccountName,Description -SearchBase "DC=REMOVED,DC=com" |
? { $_.Enabled -notlike "FALSE" } | 
Select Name,SamAccountName,Description |
Export-Csv "C:\scripts\NoDescriptionUsers.csv"

A:

You need to add another condition in your Where-Object scriptblock since you can't filter empty values with an LDAP-Query AFAIK. One suggestion:
Get-ADUser -Filter * -Properties Name,SamAccountName,Description -SearchBase "DC=REMOVED,DC=com" |
? { $_.Enabled -notlike "FALSE" -and [string]::IsNullOrEmpty($_.Description.Trim()) } |
Select Name,SamAccountName,Description |
Export-Csv "C:\scripts\NoDescriptionUsers.csv"

Personally I would also move the enabled-check into a filter in Get-ADUser to speed things up. Now the DC will only send you enabled users instead of all users. Try:
Get-ADUser -Filter { Enabled -eq $true } -Properties Name,SamAccountName,Description -SearchBase "DC=REMOVED,DC=com" |
? { [string]::IsNullOrEmpty($_.Description.Trim()) } |
Select Name,SamAccountName,Description |
Export-Csv "C:\scripts\NoDescriptionUsers.csv"

