>perl -wMstrict -MData::Dumper -le
"my $hr;
 die   'huh?' if $hr->{foo}{bar};
 print Dumper $hr;
 undef $hr;
 print 'hash ref de-init';
 die   'huh?' if exists $hr->{foo}{bar};
 print Dumper $hr;
"
$VAR1 = {
          'foo' => {}
        };

hash ref de-init
$VAR1 = {
          'foo' => {}
        };