public CurrencyUnit map(String targetNamespace, CurrencyUnit unit) {
   for (CurrencyUnitMapperSpi prov : mappers) {
     CurrencyUnit mappedUnit = prov.map(unit, targetNamespace, null);
     if (mappedUnit != null) {
       return mappedUnit;
     }
   }
   return null;
 }
 public CurrencyUnit map(CurrencyUnit currencyUnit, String targetNamespace, Long timestamp) {
   if (timestamp == null) {
     return map(targetNamespace, currencyUnit);
   }
   for (CurrencyUnitMapperSpi prov : mappers) {
     CurrencyUnit mappedUnit = prov.map(currencyUnit, targetNamespace, timestamp);
     if (mappedUnit != null) {
       return mappedUnit;
     }
   }
   return null;
 }