code: @Override
      public Geldbetrag with(MonetaryOperator operator) {
          Objects.requireNonNull(operator);
          try {
              return (Geldbetrag) operator.apply(this);
          } catch (MonetaryException ex) {
              throw ex;
          } catch (RuntimeException ex) {
              throw new LocalizedMonetaryException("operator failed", operator, ex);
          }
      }
docs: Liefert das Ergebnis des Operator <b>vom selben Typ</b>.
  
  @param operator Operator (nicht null)
  @return ein Objekt desselben Typs (nicht null)
  @see javax.money.MonetaryAmount#with(javax.money.MonetaryOperator)