code: @Nullable
    public IVATItem findVATItem (@Nullable final EVATItemType eType, @Nullable final BigDecimal aPercentage)
    {
      if (eType == null || aPercentage == null)
        return null;
      return findFirst (x -> x.getType ().equals (eType) && x.hasPercentage (aPercentage));
    }
docs: Find a matching VAT item with the passed properties, independent of the
  country.
  
  @param eType
  The VAT type to use. May be <code>null</code> resulting in a
  <code>null</code> result.
  @param aPercentage
  The percentage to find. May be <code>null</code> resulting in a
  <code>null</code> result.
  @return <code>null</code> if no matching item could be found,