Alien species living far out at the galaxy's edge, whose lawyers, students and teachers watch the crawl from a safe distance.
The nullians are the species of Quasar, Tempest, Miss Guss and Nova — an ordinary people with schools, homework assignments, plumbing, law practices and family feuds, viewing the human crawl as a piece of galactic entertainment to be written up for class credit. Tempest is described as "the young nullian", and their skin is tough enough that its condition is a normal topic of family nagging; Quasar's chief complaint about his niece is that her hands look rough and could use lotion and an exfoliating treatment.
Crucially, they live far out in the middle of nowhere. Quasar frames that as the one comfort available to him now that his client is the most hated and most watched being in the crawl: for the first time in his life he is glad of the distance. Being nullian, in other words, is currently a survival advantage.
Humanoid people with notably tough, dry hide that shows wear and benefits from moisturising, expressive enough to roll their eyes and glare.
The species from which Carl's legal representation comes, and the outside-observer perspective on the crawl.