Sometimes you do want some flow to terminate if a schema / data contract is breached, and not have this broken data contract propagate elsewhere / outwards.

And/or, it is a perfectly valid pattern to indeed add try..catch, and contain (hence "localize") the issue there and then. If there is a way to handle this breach - you will need some kind of if check anyway. Catching by matching against the particular KeyError exception is in fact robust - and if you forgot to add an intended catch, then the exception will propagate upstack, yes - which is what you want - and this way you do not need to worry about forgetting an "if None" check.

This sort of approach makes it structurally impossible to "forget" - if exception is not caught, it will abort the cannot-be-null breach continuing with program flow, possibly (e.g.) ending up persisted in some place it shouldn't be, causing problems later.