my $clientref = $job->{clientref} if (exists($job->{clientref}));
my with a statement modifier on the end is generally (almost universally?) a bad thing (unless it's a workaround for a weird issue as in ikegami's post). You probably want something like:
my $clientref = exists($job->{clientref}) ? $job->{clientref} : undef;
Update: Actually, I don't see any reason to not just do (since the value will be undef if the key doesn't exist, and it won't be autovivified in the hash):
my $clientref = $job->{clientref};
Update: ikegami is correct below. His post did not use "my...if...". My bad :-(

In reply to Re^7: panic: attempt to copy freed scalar a7b9650 to ad20598 by runrig
in thread panic: attempt to copy freed scalar a7b9650 to ad20598 by mje

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