$ perl -wle'
use Data::Dumper;
@a = qw(a);
use CGI;
my $q = CGI->new;
$q->param(-name => "foo", -values => [@a]);
print for $q->param("foo")' foo=23 foo=42
a

perl -wle'
use Data::Dumper;
@a = qw();
use CGI;
my $q = CGI->new;
$q->param(-name => "foo", -values => [@a]);
print for $q->param("foo")' foo=23 foo=42
23
42

#!/usr/bin/perl

use strict;
use warnings;
use CGI;

my $cgi = CGI->new();
my @a = ();

$cgi->param('foo',scalar @a ? @a : '');
print $_ for $cgi->param('foo');

@a = undef;

kristian@gate2:~> perl -wle '
my @a = qw(a b c);
use CGI;
my $q = CGI->new;
$q->param(-name => "foo", -values => [@a]);
print for $q->param("foo");
$q->delete("foo");
print for $q->param("foo");
'