When Nulls are a value

This is a bit of a tough one to explain but I will try - To explain the above image. Each selection of the slicer is different level of a organisation - For example a police station, Investigation Unit 1, Drug and alcohol unit - This represents one hierarchy for a single location.
The problem is that some places are put in the system as null - when I get rid of null it seems to remove a majority of the values (HR data). But from a user point of view it would be confusing for it to be called null. Are there any suggestions for changing this without removing important values/information?

Kind Regards,
Andrew