I found a small mistake in the patch, that can cause a warning (and seemingly sometimes make the entire thing segfault; SNMP.xs isn't very forgiving!). $vbl can seemingly sometimes be undef at the very end, and then scalar @$vbls of course won't work. (Curiously enough, $#$vbls, as used in the old version, actually returns -1.) Simply change the $num_vbls line to

my $num_vbls = defined($vbl) ? scalar @$vbl : 0;