FIM $importChange - Set boolean Attribute to $null

Hi,

I need to be able to set a "Person" custom attribute to NULL 

I'm using a psscript to act on a collection of users.

I can set the custom boolean attribute to $true or $false but I always have error if I try to set it to $null

The code detail is like this:

$importChange.AttributeName = “myAttributename”
$importChange.AttributeValue =$null

The error is the following:

Error = The web service client has encountered the following class of error: ValueViolatesDataTypeFormat
Details: AttributeName: myAttributename 
AttributeValue: 
Additional Text Details: The specified attribute value is in a format that cannot be stored in the attribute.

Any ideas?

Thanks,

JD