#! perl
use strict;
use warnings;
use Data::Dump;

my %testHash;                # initialize hash
my $hashRef = \%testHash;    # get a reference to that

# get a reference to an element 'a' inside the hash (that does not yet exist)
my $destref = \${$hashRef->{'a'}}; # <- problematic line

dd \%testHash;

##</code><code>##

 2:28 >perl 1389_SoPW.pl
{ a => \undef }

 2:28 >