> (a scalar that is a reference to an empty anonymous hash).
>
> However, that whole `if` block can be omitted, and you can just use
> `$changed{$params{year}}{$params{month}} = 1;`, because Perl will automatically
> (a scalar that is a reference to an empty anonymous hash).
>
> However, that whole `if` block can be omitted, and you can just use
> `$changed{$params{year}}{$params{month}} = 1;`, because Perl will automatically