i can't figure out why save_param from a session object can't seem to save keys that existed before with a undef value. a simple test shows here : (u can see that my name is gone only after assigning an empty string when saving) 
#test1.pl

#!/usr/bin/perl

use strict;
use warnings;
use CGI;
use CGI::Session qw/-ip-match/;

# instantiate a new CGI object
my $cgi = new CGI;

my $session = new CGI::Session();
my $sessionid = $session->id();

$cgi->param("myname", "max payne");

#save param into session
$session->save_param($cgi);

print "after saving, it's actually : ";
print $session->param("myname");

print $cgi->redirect( -URL     => 'test2.pl?sessionid='.$sessionid);

[download]
#test2.pl

#!/usr/bin/perl

use strict;
use warnings;
use CGI;
use CGI::Session qw/-ip-match/;

require "library.pl";

# instantiate a new CGI object
my $cgi = new CGI;
my $sessionid = $cgi->param("sessionid");

    # MARKING 1
    my $session = CGI::Session->load($sessionid);
    
    print "what was my name again >? " . $session->param("myname");
    
    $cgi->param("myname", undef);
    $session->save_param($cgi);
    
    print "<BR>(as undef) what was my name again >? " . $session->para
+m("myname");
    
    $cgi->param("myname", "");
    $session->save_param($cgi);
    
    print "<BR>(as empty string) what was my name again >? " . $sessio
+n->param("myname");

[download]
it actually outputs :
what was my name again >? max payne
(as undef) what was my name again >? max payne
(as empty string) what was my name again >?

In reply to session save_param can't save undefined value by adrive

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