use 5.012_002;
use strict;
use warnings;


my %hash = (
    this	=> 1,
    that	=> 4, 
    the	=> undef,
    other	=> undef,
    those	=> 2,
    it		=> 0,
);

# First simply disable the warning temporarily.
{
	no warnings qw/uninitialized/;
	my @warnsorted = sort { $hash{$a} <=> $hash{$b} } keys %hash;
	say "Without Warnings:\t@warnsorted";
}

# Second, check each item for definedness.
my @defsorted = sort { 
	( defined( $hash{$a} ) && $hash{$a} ) <=>
	( defined( $hash{$b} ) && $hash{$b} )
} keys %hash;

say "Testing Definedness:\t@defsorted";


# Third, sort with definedness as a criteria
my @critsorted = sort {
	defined( $hash{$a} ) <=> defined( $hash{$b} ) or
	( defined( $hash{$a} ) && $hash{$a} ) <=>
	( defined( $hash{$b} ) && $hash{$b} )
} keys %hash;

say "Defined as Criteria:\t@critsorted";

##</code><code>##

Without Warnings:	the it other this those that
Testing Definedness:	the it other this those that
Defined as Criteria:	the other it this those that

##</code><code>##

{
	no warnings qw/uninitialized/;
	my @sorted = sort {
		defined( $hash{$a} ) <=> defined( $hash{$b} ) or
		$hash{$a} <=> $hash{$b}
	} keys %hash;

	say "Defined as Criteria:\t@sorted";
}