Does this help?

#!/usr/bin/env perl 
use strict;
use warnings;

my %hash = (
    key1 => 'value',
    key2 => undef,
    key3 => {},
    key4 => { foo => 99 },
);

foreach my $key (qw(key1 key2 key3 key4)) {
    my $reftype = ref ($hash{$key});
    if ($reftype && $reftype eq 'HASH') {
        my $entries = scalar keys %{$hash{$key}};
        print "\$hash{$key} is a hashref which is " .
            ($entries ? 'not ' : '') . "empty.\n";
    } else {
        print "\$hash{$key} is not a hashref\n";
    }
}
[download]

Count the items to see if a hashref is empty or not.