[midPoint] How to remove User attribute value

[Brad Firestone]

I'm trying to figure out how to remove values from custom schema user 
attributes.

When I first started with midPoint, I thought it would be a good idea to 
create some midPoint User attribute values as part of a read-only Active 
Directory Resource.  That way when a midPoint user was created, they 
would automatically have certain attribute values.

I've since figured out that isn't the best way to do this.  I have 
removed these inbound mappings from my AD Resource.  I will now handle 
the creation/removal of these attribute values through 
assignment/inducement.

But I need to clean up these values so they are "blank".  I've tried 
lots of different combinations of things in my User Template.  I can 
change the values easily this way, but can't make it "blank".  From what 
I see in the wiki, I would think that the following mapping in my User 
Template should work, but it doesn't.

<mapping>
<name>Clear old myAttribute</name>
<authoritative>true</authoritative>
<tolerant>false</tolerant>
<strength>strong</strength>
<expression>
<value/>
</expression>
<target>
<c:path>$user/extension/myAttribute</c:path>
</target>
</mapping>

Does anyone have an idea of how I can completely clear any values from 
this midPoint User attribute?
Thanks!