sub _fill_lists {
    my ($thing, $thing_ref) = @_;

    my $class = "My::Class::$thing";                                 # <==

    if (ref $giant_hash{$thing} eq 'ARRAY') {
        for (@{ $giant_hash{$thing} }) {
            push @{ $thing_ref }, $class->new( $_ );                 # <==
        }
    } else {
        push @{ $thing_ref }, $class->new( $giant_hash{$thing} );    # <==
    }

}