Batchmode Impex Removal

Batchmode impex is poorly documented in the wiki and I've never had any luck with it. Let's say I have the following scenario:

I have 10 MyItemType with two attributes:
1. uniqueID (uid=1, 2,...,10).
2. attrOtherItemType

For MyItemType objects with uid= 1...5, their attrOtherItemType is set to null. I would like to use batchmode Impex to remove each of these instances of MyItemType. How can I accomplish this? My first instinct is to do something like this:

Remove MyItemType[batchmode=true];uniqueID[unique=true];attrOtherItemType
;;<null>

However, this spits out the following error:

value is NULL for mandatory attribute MyItemType.uniqueID

I've tried a few other things, but have had no luck. Could anyone provide some insight (and if possible, show me the correct way to implement this example)?