!defined and $_ = ' ' for @$row;

##</code><code>##

for (@$row) {
   !defined and $_ = ' ';
}

##</code><code>##

for (@$row) {
   if (!defined) {
      $_ = ' ';
   }
}

##</code><code>##

for $_ (@$row) {
   if (!defined($_) {
      $_ = ' ';
   }
}

##</code><code>##

for my $i (0..$#$row) {
   if (!defined($row->[$i]) {
      $row->[$i] = ' ';
   }
}

##</code><code>##

$_ //= '' for @$row;