The reason Hoare used the word billion was to emphasize how costly it was compared to other things. That was certainly true in C code 40 years ago and more. Those bugs were hard to find and hard to fix. In java you get a full stack trace, it's quick to fix and it doesn't come up often. Like the OP said - In practice it's not really an issue. "Worrying about nulls" is not something that most programmers do.

In C/C++ you could argue that's the case too. What's your point? My point is that fixing those bugs still costs time. It's come down in price as tooling has gotten better but the problems of a null reference remain as relevant today in languages that still use them.