Can I pass an empty Collection through impex?

Here is the sample impex.

 INSERT_UPDATE ConsumerCategory; code[unique = true]; name[lang = en]; $supercategories; $catalogversion;categoryRestrictions
 ; sample_category_1; Sample;  ;  ; ; ;

I have restrictions to make sure the category is unique under a store and a catalog revision ( I have one catalog for 20+ websites we are using restrictions to control the visibilityof categories and products per site.). I have a validator to do this.

when I create a category through HMC, an empty collection is getting passed to the validator and everything seems fine. But when I run the above impex, null is getting passed instead of an empty collection. I know I can change the validator to accommodate this, But just wanted to check if we can pass an empty List through impex somehow? I thought about writing a decorator but it returns String

Thanks -Jobin