In the previous installment of this series, we saw why the null value can be an annoying source of errors. But there are cases when you positively wish for a variable, that otherwise cannot be null, to be able to have a null value. Imagine, for example, a web site that stores the last time each user has logged in. public class User { public string NickName { get; set; } public string Email { get; set; } public string PasswordHash { get; set; } public DateTime LastLoginTime { get; set; } } If a user has just registered but they haven’t yet logged in, we want the LastLoginTime property to be somehow empty.