$rec{NOTE}{Nested}

##</code><code>##

$rec{NOTE}->{Nested}

##</code><code>##

( $rec{NOTE} //= {} )->{Nested}

##</code><code>##

use strict;
use warnings;
no warnings 'void';

my %rec;

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;
print "--\n";

$rec{NOTE} = undef;

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;
print "--\n";

$rec{NOTE}{Nested};

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;

##</code><code>##

exists:  0
defined: 0
true:    0
--
exists:  1
defined: 0
true:    0
--
exists:  1
defined: 1
true:    1