if ($rec{NOTE­} && exists $rec{NOTE}­{Nested}) {
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More-DRY versions:

if(  exists ${ $rec{NOTE­} || {} }{Nested}  ) {
# or
if(  ( $rec{NOTE­} || {} )->{Nested}  ) {
# or
if(  exist +( $rec{NOTE­} || {} )->{Nested}  ) {
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Though, I find that I use those less often to avoid auto-viv and more often to prevent a potential fatal "Can't use undef as HASH ref" (something that I think should at least be turned into just a warning -- since sometimes it is fatal and sometimes it is a silent success, and I'm not even sure what distinguishes between those two behaviors).