Spree::Zone#country_list fix
Spree::Zone#country_list fix

Just fixing wrong default value of case expression - should return an Array instance, ie. `[]` instead of `nil`.

Fixes #4827

dotandbo/spree,yomishra/pce,dotandbo/spree,yomishra/pce,dotandbo/spree,dotandbo/spree,yomishra/pce