$ perl -Mstrict -MData::Dumper -wE '
my $h; $h->{foo}->{bar}->{baz} = "qux";
say Dumper $h;
say( (exists $h->{foo}->{bar}->{baz}) ? 1 : 0 );
say( (exists $h->{foo}->{NOT} && exists $h->{foo}->{NOT}->{baz}) ? 1 : 0 );
say Dumper $h;
'
$VAR1 = {
          'foo' => {
                     'bar' => {
                                'baz' => 'qux'
                              }
                   }
        };

1
0
$VAR1 = {
          'foo' => {
                     'bar' => {
                                'baz' => 'qux'
                              }
                   }
        };