code: public ExchangeRate getReversed(ExchangeRate rate){
          ConversionQuery reverseQuery = rate.getContext().toQueryBuilder().setBaseCurrency(rate.getCurrency())
                  .setTermCurrency(rate.getBaseCurrency()).build();
          if(isAvailable(reverseQuery)){
              return getExchangeRate(reverseQuery);
          }
          return null;
      }
docs: The method reverses the {@link javax.money.convert.ExchangeRate} to a rate mapping from term
  to base {@link javax.money.CurrencyUnit}. Hereby the factor must <b>not</b> be
  recalculated as {@code 1/oldFactor}, since typically reverse rates are
  not symmetric in most cases.
  
  @return the matching reversed {@link javax.money.convert.ExchangeRate}, or {@code null}, if
  the rate cannot be reversed.