@Override
 public int compare(ProductOfferId o1, ProductOfferId o2) {
   return NULLS_LAST_CASE_INSENSITIVE_ORDERING.compare(o1.getValue(), o2.getValue());
 }
 /**
  * Creates a new ProductOfferId.
  *
  * @param offerId may be null if creating an "other" dimension
  */
 public static ProductOfferId createOfferId(@Nullable String offerId) {
   ProductOfferId productOfferId = new ProductOfferId();
   productOfferId.setValue(offerId);
   return productOfferId;
 }