code: @Override
      public String selectMajorCurrency(final String ccy1, final String ccy2) {
          return ranks.getOrDefault(StringUtil.toUpperCase(ccy1), DEFAULT_UNRANKED_VALUE).intValue() <= ranks.getOrDefault(StringUtil.toUpperCase(ccy2), DEFAULT_UNRANKED_VALUE).intValue() ? ccy1
                  : ccy2;
      }
docs: Given 2 currencies, return the major one if there is one, otherwise returns the first currency.