Comment by ccouzens

There are other ways, like having a null with more regular semantics and better composeability (like Rust's option type).

Or imagine this data:

Students:

Name: Bob

Name: Alice

StudentsClasses

Student: Bob, class: cryptography.

Student: Bob, class: databases

If you can have arrays (or relations) as a field in your result set, then

Students left outer join StudentsClasses

Could return

Student: Bob, classes: [ cryptography, databases]

Student: Alice, classes: []