Too much typing, you could do with a one-liner instead. I ++'ed you anyhow because the idea is good. ;-)

use strict;
use Data::Dumper;

my $rec = [ undef, 1, '', 2, 0 ];

@$rec = map { defined($_) ? $_ : '' } @$rec;

print Dumper($rec);

__END__

# ---output ---
$VAR1 = [
          '',
          1,
          '',
          2,
          '0'
        ];
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