code: @Override
      public Set<String> getProviderNames() {
          Set<String> result = new HashSet<>();
          for (CurrencyProviderSpi spi : Bootstrap.getServices(CurrencyProviderSpi.class)) {
              result.add(spi.getProviderName());
          }
          return result;
      }
docs: Access a list of the currently registered providers. Th names can be used to
  access subsets of the overall currency range by calling {@link #getCurrencies(String...)}.
  
  @return the currencies returned by the given provider chain. If not provider names are provided
  the default provider chain configured in {@code javamoney.properties} is used.