Thank you for the suggestions. I have reported a bug on CPAN, with a more complete example.

perl -we 'use Safe; use Safe::Hole; printf("%s, %s\n", $Safe::VERSION,
+ $Safe::Hole::VERSION); use JSON; my $safe = Safe->new; my $hole = ne
+w Safe::Hole {}; sub w() { print "In wrapped w() subroutine.\n"; retu
+rn $hole->wrap(JSON->new); } $hole->wrap(\&w, $safe, "&w"); print "Th
+is should fail:\n"; $safe->reval("sub x { return \&w; } f(x());"); pr
+int "It succeeded\n" unless($@);'
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2.35, 0.10
This should fail:
In wrapped w() subroutine.
Use of uninitialized value $typechar in string eq at /usr/lib64/perl5/
+vendor_perl/Safe/Hole.pm line 121.
It succeeded
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