code: public ConversionQueryBuilder setRateTypes(RateType... rateTypes) {
          return set(ConversionQuery.KEY_RATE_TYPES, new HashSet<>(Arrays.asList(rateTypes)));
      }
docs: Set the providers to be considered. If not set explicitly the <i>default</i> ISO currencies as
  returned by {@link java.util.Currency} is used.
  
  @param rateTypes the rate types to use, not null.
  @return the query for chaining.