Java singleton using enum and hashmap

singleton_enum.java

public enum DomesticShipment {
   INSTANCE;
   private Map<String,String> domesticCountry;

   DomesticShipment() {
      domesticCountry = new HashMap<>();
      domesticCountry.put("ausPost","AU");

   }

   public boolean isDomestic(String carrierType, String country) {

      return domesticCountry.containsKey(carrierType) &&
              domesticCountry.get(carrierType).equalsIgnoreCase(country);
   }

}

To use: 
DomesticShipment.INSTANCE.isDomestic(carrier, destinationCountry);