The rule in Java, enforced by the programmer, not the compiler, is that you never assign an Optional to null. If a method returns Optional, you're free to assume it will never return null. If it does, you should track down and publicly shame the author of such monstrosity.
"If you do that, ideally, a small gnome climbs out the back of the computer and hits the developer with a mallet."
(various bits of perl IRC have adopted the mallet gnome as an idiom over the years and it seems to convey the "please don't" point without being overly combative ;)
