code: public ExchangeRateBuilder toBuilder() {
          return new ExchangeRateBuilder(getContext()).setBase(getBaseCurrency()).setTerm(getCurrency())
                  .setFactor(getFactor()).setRateChain(getExchangeRateChain());
      }
docs: Create a {@link ExchangeRateBuilder} based on the current rate instance.
  
  @return a new {@link ExchangeRateBuilder}, never {@code null}.