public class Example{
    // Return null to indicate an empty collection. Don't do this!
    /**
    * @return list containing all of the cheeses in the shop,
    * or null if no cheeses are available for purchase.
    */
    public List<Cheese> getCheeses(){
        return cheeseInStock.isEmpty() ? null : new ArrayList<>(cheesesInStock);
    }
}

if (cheeses != null) // سيحتاج هذا السطر كثيراً

public List<Cheese> getCheeses() {
    return new ArrayList<>(cheesesInStock);
}

// Optimization - avoid allocating empty collections
public List<Cheese> getCheeses() {
    return cheeseInStock.isEmpty() ? Collections.emptyList() : new ArrayList<>(cheesesInStock);
}

// The right way to return a possibly empty array
public Cheese[] getCheeses() {
    return cheeseInStock.toArray(new Cheese[0]);
}