code: @Override
      public List<String> getDefaultProviderChain() {
          List<String> provList = new ArrayList<>();
          String defaultChain = MonetaryConfig.getConfig().get("currencies.default-chain");
          if(defaultChain!=null) {
              String[] items = defaultChain.split(",");
              for (String item : items) {
                  if (getProviderNames().contains(item.trim())) {
                      provList.add(item);
                  } else {
                      Logger.getLogger(getClass().getName())
                              .warning("Ignoring non existing default provider: " + item);
                  }
              }
          }
          else{
              Bootstrap.getServices(CurrencyProviderSpi.class).forEach(
                      p -> provList.add(p.getProviderName())
              );
          }
          return provList;
      }
docs: This default implementation simply returns all providers defined in arbitrary order.
  
  @return the default provider chain, never null.