#####
use Data::Dumper;$Data::Dumper::Indent=0;
my $n = {};
for (@{$n->{'x'}}) {
        print 1;
}
print Dumper ($n), "\n";
#####

Output:

#####
$VAR1 = {'x' => []};
#####

# the same throws exception:
# Can't use an undefined value as an ARRAY reference
@{$$n{'y'}} and print 2;