A null pointer error is basically what happens when a computer program tries accessing information that does not exist, and ends up glitching out or crashing as a result. This happens because a pointer — which is a piece of information that basically just tells the computer where in memory it can find another piece of information — has been set to point to a nonexistent location in memory, known as "null", hence a "null pointer". Null pointers do actually have plenty of perfectly valid uses in computer programming — the problem happens when the computer for one reason or another ends up taking the null pointer saying "I am pointing to nowhere in particular" as meaning "hey let's go to this cool place called Nowhere in Particular, you'll totally find the information you're looking for there".

In context, I made up the term "ethnic null pointer error" to refer to the experience of being pushed to perform or identify with being American, as a member of the American diaspora. Because you can't really answer questions like "what's American cuisine?" or "what's American handicrafts?" or "what's the American national costume?" et cetera, right? If a bit of "American culture" wasn't stolen, or rooted in puritanical religious fundamentalism, or invented by a capitalist to sell plastic crap, it's probably already become too popular worldwide due to cultural imperialism to even stand out as an American thing. So as a member of the American diaspora, you don't really have much of anything that you could claim as "your culture", even when the circumstances are very much pushing you to look for something to claim.