The problem with NULL is that it is forcibly adjoined as a value the compiler considers valid to every pointer type. In the languages in question, you can't hav

The problem with NULL is that it is forcibly adjoined as a value the compiler considers valid to every pointer type. In the languages in question, you can't have a non-nil pointer, no matter how much you might want one. I do agree that it is, on its own, not necessarily the large problem it is made out to be. One nice thing about NULL dereferences is that they tend to be visible and obvious. They crash things and make lots of noise. As invalid values go, they're actually on the friendlier side. The invalid values that silently sail through your program, corrupting everything they touch, but never crashing anything, are far more dangerous. In fact one of the worst possible solutions to a NULL is to default it to some value, especially one like "0" that looks like half the other values in your program. The dangers of NULL are somewhat oversold because they are cognitively-available dangers. We see the crashes. We see the failures. But those are far better than the failures we don't see, and the crashes we see only much later, sometimes years later. (Don't ask me about the legacy billing systems I've been trying to deal with.) But was it a billion dollar mistake? Still yes, because having a type that forces this value on to the legal set is still a mistake and has still caused lots of problems that could have been avoided. In addition to that billion dollar mistake, there has also been a lot of code written that has made similar mistakes of allowing similarly illegal values representable in the code, and that has also been a huge mistake. Perhaps a larger one, perhaps not. Hard to get an objective measure of these two mistakes, both huge, both frequent, both highly impactful. Ultimately, though, the NULL pointer is just a particular instantiation of the general problem of allowing illegal states to be represented, and of that class of problem, it is probably one of the least harmful examples of it... unless you overly avail yourself of all of those "a?.b?.c?.d" operators and "upgrade" your NULL issues into something that sprays illegal and/or incorrect values through your code instead. I really don't like those things being so convenient to hand, they encourage people to jump from the frying pan into the fire too often.