The problem is with exists creating intermediate levels

Note that, if you consider this to be a problem you can install the autovivification module, then specify no autovivification to prevent it:

#!/usr/bin/env perl    

use strict;
use warnings;
use 5.010;

no autovivification;

use Data::Dumper;
my %hash = ( a=>{} );
if (  !exists $hash{'a'}{'b'}{'c'} ){};
print Dumper \%hash;
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Output:

$VAR1 = {
          'a' => {}
        };
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This is, however, apparently not an option for the OP, due to short-sighted customer requirements and autovivification is an XS module, so using its code independently of the original module would be a bit more involved than just copy/pasting the source.