I had a look at DBI::Changes, and nothing jumped out at me, but you might have better luck since you know your environment better than I do.

I notice you're calling fetchrow_array in a scalar context, which the DBI documentation says is a bad idea for various reasons. I'd make that line be:

($imm) = $immh->fetchrow_array;
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That said, I don't see why the code you have wouldn't work as it is.

The only other suggestion I have is to set the RaiseError attribute on your database handle. It'll save you from checking for errors all the time, and you'll know if fetchrow_array (in scalar context) is returning a NULL from the database or undef because it had a problem.