Select Code to Download

<form>
<input type="checkbox" name="passenger" value="somevalue" />
<input type="submit" name=".submit" value="OK">
</form>

use strict;
use warnings;
...
$set_value = $mech->value($target_field);
$set_value = 'undef' unless defined $set_value;
print "[2] value for $target_field: ($set_value)\n";

$ perl tick.pl http://localhost/form.html
[1] value for passenger: (undef)
[2] value for passenger: (somevalue)