You can still have “the absence of a value”, but it’s codified in the type system. Most languages with this feature implement an Optional or Maybe wrapper type,

You can still have “the absence of a value”, but it’s codified in the type system. Most languages with this feature implement an Optional or Maybe wrapper type, that is either Some<T> or None (i.e. no value). The difference is, because you’re now receiving a different type, you are forced to deal with the case where there’s no value. Rather than your function returning a Customer that could sometimes be null—and if it’s only null infrequently, you’re much more likely to forget to handle it—it instead returns Optional<Customer>. To operate on that Customer object, you are forced to unwrap the Optional by checking whether the underlying value is there. How well you handle the None case is up to you, but the compiler won’t let you forget (generally anyway; for example Swift allows you to force-unwrap optionals with a crash on the None case, but eh).