use XML::Simple;

my $xml=<<'EOXML';
<config logdir="/var/log/foo/" debugfile="/tmp/foo.debug">
  <groups></groups>
  <age>18</age>
  <weight>220</weight>
  </config>
EOXML

my $xs  = XML::Simple->new;
my $ref = $xs->XMLin($xml);

use Data::Dumper;

warn Dumper($ref);



##</code><code>##


[tbrannon@devel tmp]$ perl xml-simple.pl
$VAR1 = {
          'debugfile' => '/tmp/foo.debug',
          'weight' => '220',
          'groups' => {}, #### <---- want empty string here!
          'age' => '18',
          'logdir' => '/var/log/foo/'
        };