NUnit.Samples.Money.MoneyBag.AppendMoney C# (CSharp) Method

        private void AppendMoney(Money aMoney)
        {
            IMoney old= FindMoney(aMoney.Currency);
              if (old == null) {
            fMonies.Add(aMoney);
            return;
              }
              fMonies.Remove(old);
              IMoney sum= old.Add(aMoney);
              if (sum.IsZero)
            return;
              fMonies.Add(sum);
        }

        public IMoney Negate()
        {
            MoneyBag result = new MoneyBag();

            foreach (Money m in fMonies)
            {
                result.AppendMoney((Money)m.Negate());
            }
            return(result);
        }