Perl does this automatically, it's called autovivification.

You only have an issue if you want to avoid it.

update

hmm thats the problem if you post from a mobile client without possibility to test...

I'll update a working solution, though using Data::Diver should help already.

update

use warnings;
use strict;
use Data::Dumper;

my @keys="a".."d";
my %hash=();
my $href=\%hash;

my $lastkey= pop @keys;

for my $key (@keys) {
  $href =
    $href->{$key} //= {} ;
}

$href->{$lastkey} = "";

print Dumper \%hash;
[download]

--->

$ perl dive.pl 
$VAR1 = {
          'a' => {
                   'b' => {
                            'c' => {
                                     'd' => ''
                                   }
                          }
                 }
        };
[download]

update

fixed bug