I think they're making the distinction between special cases and error cases. An empty list could be valid(e.x. a search of users providing no results) so you

I think they're making the distinction between special cases and error cases. An empty list could be valid(e.x. a search of users providing no results) so you still need to differentiate between "special cases that need special logic" and "bad input". Lumping the two together in one `if` block makes any code less readable imo, because they're not the same thing.