Script to Trim ending spaces in active directory users attributes.

Trying to get a script to work to delete the spaces in some of our users extentionAttribute6 entries.

Get-aduser -filter [extensionAttribute6 -like "*"} | Foreach {Set-aduser -Identity $_.extensionAttribute6 $_.extensionattribute6.TrimEnd()}

I get a "You cannot call a method on a null-valued expression" Error.

Any help would be appreciated!