Is instantiating a collection in a domain model considered a good practice?

I see these types of model is many samples online.

public class User
{
    public long Id { get; set; }
    public string Name{ get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

Is it considered a good practice to instantiate a collection in the constructor like the code below? If so what are the reasons? How about objects in the model?

public class User
{
    public User()
    {
        Products = new List<Product>();
    }
    public long Id { get; set; }
    public string Name{ get; set; }
    public virtual ICollection&开发者_Python百科lt;Product> Products { get; set; }
}

Well, I would say it depends on the situation, but Products in this case would be filled from the database, via a repository, so most probably ORM of some sort, so no initialization to new List would be needed in the constructor. The meaning of null for Products is indicative that the list isn't loaded yet. On the other hand, let's say that your object must have this collection initialized. For simple objects DDD says constructors are perfectly fine to to these things, but in case of complex objects, move the construction to the Factory.