code: public static Collection<String> getFormatProviderNames() {
          Collection<String> providers = Optional.ofNullable(getMonetaryFormatsSpi()).orElseThrow(
                  () -> new MonetaryException(
                          "No MonetaryFormatsSingletonSpi loaded, query functionality is not available."))
                  .getProviderNames();
          if (Objects.isNull(providers)) {
              Logger.getLogger(MonetaryFormats.class.getName()).warning(
                      "No supported rate/conversion providers returned by SPI: " +
                              getMonetaryFormatsSpi().getClass().getName());
              return Collections.emptySet();
          }
          return providers;
      }
docs: Get the names of the currently registered format providers.
  
  @return the provider names, never null.