perl -MData::Dumper -we 'print Dumper $h1 unless $h1->{a}->{b}->{c}'
$VAR1 = {
          'a' => {
                   'b' => {}
                 }
        };

##</code><code>##

perl -MData::Dumper -we 'print Dumper $h1 for $h1->{a}->{b}->{c}'
$VAR1 = {
          'a' => {
                   'b' => {
                            'c' => undef
                          }
                 }
        };