Thanks ikegami but I'm still not quite understanding this but I certainly appreciate your help. In your example you've used $x for the "workaround". I don't understand why I have to do this. Perhaps it would be easier if I posted the exact code (comments labelled MJE I added):

sub queue_job
{
    my ($betdb, $q, $job) = @_;
    my $key;

    $job->{jobid} = new_job_id($betdb);

    # MJE - obviously this can be undef but in the case in
    # question it is usually set
    my $clientref = $job->{clientref} if (exists($job->{clientref}));

    #
    # Insert info about this job in the audit file.
    # NOTE: This will fail if we've seen this client_reference before 
+as
    # client_reference is unique and it would indicate a client has su
+bmitted
    # the same job twice e.g. posted the same job twice.
    #
    my $caught = try {
        my $repost = $clientref ? 0 : undef;

        $betdb->execProc(
            $p_run_or_queue_job,
            {DieOnError => 1, Comment => 'queue_job'},
            $job->{jobid}, $clientref,
            $job->{sessionid}, $job->{name},
            {clob => $json->objToData($job)},
            $repost, 1);
        0;
    } catch {
        my $ev = $_;
        if (($betdb->getDBh())->err == 1) {   # constraint violation
            eval {
                $betdb->callPkgProc(
                    {DieOnError => 1, Comment => 'run_now'},
                    BET::DB::SYN_PKG_BETDB,
                    'p_invalidJobRequest',
                    $job->{jobid},
                    $clientref,
                    $job->{sessionid},
                    $job->{name},
                    $json->objToData($job->{args}),
                    R_DIE,
                    "Job already seen");
                1;
            } or $log->warn("Failed to mark job already seen - $@");
            $job->{joberr} = 'Already seen this job';
            $job->{jobnative} = c_JOB_ALREADY_SEEN;
            $log->warn(sub {'JOB ALREADY POSTED ' . Dumper($job)});
        } else {
            $log->logwarn("Failed to insert into job_audit, $ev");
        }
        1;
    };
    return if $caught;
    my @now = gmtime(time());
    $job->{jobqed} = sprintf "%d/%d/%d %02d:%02d:%02d",
      $now[3], $now[4]+1, $now[5]+1900, $now[2], $now[1], $now[0];

    push @{$q->{jobs}}, $job;
    $q->{queued}->{$key} = $job->{jobid} if ($key);
    $log->debug("Queued job " . $job->{jobid});
    $total_jobs_on_all_queues++;
    return $job->{jobid};
}
[download]

$clientref if the scalar which 5.10.1 complains about.

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