public void writePriceForQuantity (int productPackQuantity, BigDecimal price) {
		if (price==null) {
			throw new NullPointerException("Arguments can't be null");
		}

		// (price==0) - up to upper system level

		// (productPackQuantity==0) - up to upper system level

		if (!prices.containsKey(productPackQuantity)) {
			prices.put(productPackQuantity,price);
		}

		else {
			prices.remove(productPackQuantity);
			prices.put(productPackQuantity,price);
		}

	}