> Most people have still written code for school or a hobby project. Maybe I'm missing empathy, but I cannot understand how some developers have no code to show.

First: they might have private code, but not necessarily code to show (I, for example, am rather not willing to show quite some of the code that I wrote privately).

Second: the kind of "code" that I tend to write privately (and into which I invest quite a lot of time) is really different from what I do at work, and what is actually considered "code" by many. It's more like (very incomplete) drawings and TeX notes about observations and proofs of properties and symmetries between some algorithms. Once finished, they will be very easy to systematically transform into a program in a computer language.

This is about very novel stuff, which to explain would take quite a lot of time.

The objective in an interview like this shouldn't be to grade the quality of the code you bring in any sort of scale, but to have a discussion about the options you took. In that sense, it really matters very little what you present as long as we can do a small back-and-forth that lets me into what sort of person you are.