... there were a few undef elements in the rowcache.

Use of warnings would have enabled Perl to alert you to this situation, and
    use warnings FATAL => 'all';
would have put a quick and merciful end to it.

c:\@Work\Perl>perl -wMstrict -le
"use warnings FATAL => 'all';
 ;;
 my $hr = { foo => 'bar' };
 my @ra = ($hr, $hr, undef, $hr, $hr);
 ;;
 for my $hashref (@ra) {
   print qq{foo is '$hashref->{foo}'};
   }
"
foo is 'bar'
foo is 'bar'
Use of uninitialized value in concatenation (.) or string at -e line 1
+.
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