code: public Coupons getUniqueCouponCodes(final String couponCode, final QueryParams params) {
          return doGET(Coupon.COUPON_RESOURCE + "/" + couponCode + Coupon.UNIQUE_CODES_RESOURCE,
                  Coupons.class, params);
      }
docs: Lookup all unique codes for a bulk coupon given query params.
  
  @param couponCode String coupon code
  @param params {@link QueryParams}
  @return the unique coupon codes for the coupon code on success, null otherwise