use strict;
use warnings;

use Test::More tests => 2;

my $have = '1,,3,4,,,';
my @want = (1, undef, 3, 4, undef, undef, undef);

my @try = map { length ($_) ? $_ : undef } split (',', $have, -1);

is_deeply \@try, \@want, 'Array is correct';

# Your criterion
my $count = 0;
foreach (@try) {
    ++$count;
}

is $count, 7, 'Count is correct';