Are you having challenges with the Get-ADUser commandlet not pitching errors on a -Filter producing $null results?  Intuitively, it would make sense for the -Filter to filter those out with a -ne $null.  Well, it doesn’t work that way.  There is a Where-Object commandlet that one can pipe to  and filter out those things.  In my example, I chose to filter out $null User Principal Names.  Here’s the example:

$myNonNullUsers = Get-ADUser -Filter { enabled -eq $true } -Properties * | Where-Object {$_.userPrincipalName -ne $null}