Registry value conditional using Location Awareness

Trying to use Location awareness and a conditional based on a registry key. I want to check for a specific value, OR the existence of a Key Name, OR if the value is BLANK. I have not been able to create a condition that will evaluate a blank value. I have tried " " and it does not work correctly. I can not save that condition without inputting some value in the field.
I need to be able to create a condition for a BLANK key value.