When your object goes out of scope, perl looks for a sub DESTROY in your module. Since you haven't defined one, the AUTOLOAD method takes over. Your AUTOLOAD method then checks to see if your object has a field by the same name of the method call and die's if it doesn't.

You can do a couple different things. First, you could add a DESTROY stub so that the AUTOLOADER doesn't come into play:

sub DESTROY {}
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or you can change your sub AUTOLOAD so that it ignores this method call that perl does automatically:

my $name = $AUTOLOAD;
$name =~ s/.*://;   # strip fully-qualified portion

# this is new...
return 0 if($name eq 'DESTROY');

unless (exists $self->{_permitted}->{$name} ) {
    croak "Can't access `$name' field in class $type";
}
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That should take care of the error.
Update Looks like I was a bit late in my reply as someone else already suggested the sub DESTROY {} solution... Oh well