use 5.010;
use strict;
use Data::Dumper;

my %rec;

{
	no autovivification;
	
	say "Oh No!(1)" if exists $rec{NOTE}{Nested};
	say "Oh No!(2)" if exists $rec{NOTE};
}

say "Oh No!(3)" if exists $rec{NOTE2}{Nested};
say "Oh No!(4)" if exists $rec{NOTE2};

print Dumper \%rec; 

__END__
Oh No!(4)
$VAR1 = {
          'NOTE2' => {}
        };

##</code><code>##

no autovivification qw(exists);
if (!exists $rec{NOTE}{Nested})
{
  # but this still autovivifies $rec{NOTE}={};
  $rec{NOTE}{Nested2} = 'Foo';
}