Subtraction between two dates in Powershell is evaluating to null - powershell

Question

I am using the following code to display some values , the subtraction between two dates as in the expression
[datetime]::Now.AddDays(-365) - $_.PasswordLastSet).Days
is evaluating to null in my data, what could be the reason, how to fix this code ?
Get-ADUser -Filter * -Properties PasswordLastSet, Mail -SearchBase $searchBase |
Where-Object{
([datetime]::Now.AddDays(-365) - $_.PasswordLastSet).Days -in #(" ",364, 350, 354, 340, 335,' ','',"")
}|
Select-Object name, PasswordLastSet,#{n='DaysUntilExpired';e={(([datetime]::Now.AddDays(365) - [datetime]::$_.PasswordLastSet).Day).days}} |
Add-Content -Path C:\Temp\PasswordExpList.txt

Answer 1

There are two obvious bugs in your code, both here:
#{n='DaysUntilExpired';e={(([datetime]::Now.AddDays(365) - [datetime]::$_.PasswordLastSet).Day).days}}
However, I can't tell if you should specify this:
#{n='DaysUntilExpired';e={([datetime]::Now.AddDays(365) - $_.PasswordLastSet).Days}}
Or, if you're looking for the last day of the month prior to the expiration date, then this:
#{n='DaysUntilExpired';e={(([datetime]::Now.AddDays(365) - $_.PasswordLastSet.Day).Days}}
As the comments mention, [datetime]::$_.PasswordLastSet is nonsense. That's the first bug. The second one is that the property of a timespan is Days, not Day. Day is a property of a datetime.
However, assuming you're trying to calculate the password expiration date defined by AD password policy, you should look at the msDS-UserPasswordExpiryTimeComputed property in AD because that's what that property contains. You have to convert it from a large integer date, but that's what [datetime]::fromfiletime() does.
Get-ADUser -Filter * -Properties PasswordLastSet, Mail, 'msDS-UserPasswordExpiryTimeComputed' -SearchBase $searchBase |
Select-Object -Properties Name, PasswordLastSet, #{n='PasswordExpirationDate';e={[DateTime]::FromFileTime($_.'msDS-UserPasswordExpiryTimeComputed')}}
This doesn't do everything your script does, but then I don't understand why you're looking for accounts whose password was set an exact number of days in the past. That doesn't seem useful.