Facebook / Meta had their own string type which did this, turns out now you have an exciting bug because you end up assuming uninitialized values have properties but they don't, reading an uninitialized value is Undefined Behaviour and so your stdlib conspires with the OS to screw you in some corner cases you'd never even thought about because that saved them a few CPU cycles.

The bug will be crazy rare, but of course there are a lot of Facebook users, so if one transaction out of a billion goes haywire, and you have 100M users doing 100 transactions on average, the bug happens ten times. Good luck.