code: public Optional<String> findCommonCcy(final CurrencyPair otherPair) {
          if (containsCcy(otherPair.getCcy1())) {
              return Optional.of(otherPair.getCcy1());
          }
          return containsCcy(otherPair.getCcy2()) ? Optional.of(otherPair.getCcy2()) : Optional.empty();
      }
docs: Given another CurrencyPair find the common Currency (if any) or the first if both are identical
  @param otherPair
  @return the common ccy or Empty optional