第43条：返回零长度的数组或者集合，而不是null

private final List<Cheese> cheesesInStock = ...;

public Cheese[] getCheese() {
    if(cheesesInStock.size() == 0)
        return null;
    ...
}

Cheese[] cheeses = shop.getCheeses();
if(cheeses != null && Arrays.asList(cheese).contains(Cheese.STILTON))
    System.out.println("Jolly good");
}

Cheese[] cheeses = shop.getCheeses();
if( Arrays.asList(cheese).contains(Cheese.STILTON))
    System.out.println("Jolly good");
}

public List<Cheese> getCheeseList() {
    if(cheeseInstock.isEmpty)) {
        return Collections.emptyList();
    else
        return new ArrayList<Cheese>(cheesesInStock);
}