Instead it returns nothing.

If you use strict and warnings you will get something -- an error message.

wfsp is correct. Dumpvalue may also be useful when you're trying to remember how to dereference because it shows the numeric indexes of arrays (How can I visualize my complex data structure?):

use warnings;
use strict;
use Dumpvalue;

my $res1 = {
        'report' => [
                     '2011-01-25 10:30:50',
                     {
                       'AntiVir' => 'Eicar-Test-Signature'
                     }
                    ]
        };

Dumpvalue->new->dumpValue($res1);

__END__

'report' => ARRAY(0x60b0f0)
   0  '2011-01-25 10:30:50'
   1  HASH(0x60b220)
      'AntiVir' => 'Eicar-Test-Signature'
[download]

An alternate approach is to use Data::Diver:

use warnings;
use strict;
use Data::Diver qw(Dive);

my $res1 = {
        'report' => [
                     '2011-01-25 10:30:50',
                     {
                       'AntiVir' => 'Eicar-Test-Signature'
                     }
                    ]
        };

print Dive( $res1, qw( report 0 ) ), "\n";
print Dive( $res1, qw( report 1 AntiVir ) ), "\n";

__END__

2011-01-25 10:30:50
Eicar-Test-Signature
[download]