I'm a little paranoid when I deal with CGI parameters. Sometimes I do something like the following (note the or test is untested -- I usually get precedence wrong the first time):

my @expected = qw( title requester department etc );
my @request;
foreach my $expect (@expected) {
    push @request, ($q->param($expect) or '0');
}
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What you could do is put the B1 .. B6 parameters in a separate array and do the or 0 trick on them. Put the other parameters in the first array and do something like this:

foreach my $expect (@expected) {
    my $received = $q->param($expect);
    unless (defined $received) {
        $error .= "Didn't get $expect parameter!\n";
        last;        # and do an error somewhere
    }
    push @request, $received;
}
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This way, you don't have a malicious HTML hijacker pass bad data and have it end up in your file somewhere. Plus, you get to check immediately.

Update: isotope makes a good point below. A little client-side JavaScript is good for verifying submissions, but some users have it disabled (for good reason), and my point about not trusting the client still applies. Just be friendly about it, as isotope recommends.