code: public FxRateCalculatorBuilder ratesSnapshot(final Collection<FxRate> rates) {
          if (rates != null) {
              this.ratesSnapshot.clear();
              this.ratesSnapshot = rates.stream().collect(Collectors.toMap(FxRate::getCurrencyPair, t -> t));
          }
          return this;
      }
docs: Snapshot of FxRate, typically they are the Base FX Rates (e.g. vs USD)
  @return the builder