What happens when you need an "else" branch?
Is not having a person for the given ID an error, is it a "do nothing", or does it mean to create a new person?
What does the callback version do if you forget to make your index unique, and end up with multiple people with the same ID; does it get run multiple times? The version that returns a Maybe<Person> at least has an obvious proper response (throw an error).
Attention is a limited commodity, and I think it's worth preserving for the important things. Sometimes it really is worth reminding people, "Hey, this could be null!" But a lot of the time that is boring.
To me this often comes back to favoring meaning over mechanism. The higher up I go in code, the more I want it to be about what the system means, not the particular mechanism I've chosen to make it work. E.g., Computers may be implemented via impure silicon, but most of the time we can forget that. I try to apply that to any sort of mechanism.
Then you use one, but null checks generally aren't cases of if/else conditionals, they're more along the lines of "either I have one or mayday mayday". Sometimes slightly softened into "either I have one or use this default thing"
That would be the Perl way of
my $person = $data_source->get_person($id) or die "No person available";
Any ideas?