$ perl -MData::Dumper -wle 'my %a; print defined $a{1}{2}; print Dumper \%a;'

$VAR1 = {
          '1' => {}
        };


$ perl -MData::Dumper -wle 'my %a; print exists $a{1}{2}; print Dumper \%a;'

$VAR1 = {
          '1' => {}
        };