Detect null object in powershell: - powershell

Question

I am working on implementing some user creation in active directory using the built in powershell commandlets, recently I came across this issue. When attempting to read in a data file of users where $_.UID is one of the fields in the file, I do a Get-ADUser with the UID to check if the user already exists in ldap. If I get a null object, then I would like to create the user because this id is not already in ldap otherwise I would like to skip the entry in the datafile. My script as is creates the users the first time through. If I run it a second time on the same data file (users should no longer be null for the UID field) the if condition is still true and the script attempts to create users a second time. I am new to powershell scripting so I must be misunderstanding something. What am I doing wrong? Your help is appreciated!
Function createUsers{
Import-CSV "~\Desktop\inData.csv" | ForEach-Object {
$USER = Get-ADUser -LDAPFilter "(uid=$_.UID)"
if($USER -eq $Null){ #BROKEN DOESN'T DO ANYTHING
#(!$USER) Doesn't work either
Write-Host "Making next user."
.
.
.
}else{
Write-Host "Skipping, user exists!!"
}
}
}

Answer 1

I think that your problem is in your Get-ADUser Query. There is no property called "uid" in Active Directory. This will make $USER always null, and cause it to always want to create a new user.
Try using sAMAccountName instead:
$User = Get-ADUser -LDAPFilter "(sAMAccountName=$_.UID)"
To get a full list of all the properties available to you, I like to execute the following:
Get-ADUser MyUserName -Properties *