#!/usr/bin/env perl -l

use strict;
use warnings;

my %multi = (empty => {}, data => { a => 1 });

for my $key (keys %multi) {
    if (keys %{$multi{$key}}) { 
        print "Data found in $key";
    }
    else {
        print "Data not found in $key";
    }
}

##</code><code>##

$ pm_1129100_complex_hash_check.pl
Data found in data
Data not found in empty