%H = ( 'x' => 'y', 'y' => $undef_var, 'z' = 'a' );

##</code><code>##

#!/usr/bin/perl

%p = (
      'a' => 'B',
      'z' => defined($x) ? $x : '',
      'c' => 'D');

use Data::Dumper;
#warn Data::Dumper->Dump([\%p],['p']);
warn $p{z};