I wonder if you realise exactly what it is that you are testing with this construct? :)

use strict;
use warnings;

$" = '+';

for( 
    ['a', 'b'], 
    [1, 2], 
    [0, 1], 
    ['a', 'b'], 
    [undef, undef], 
    [1, undef], 
    [undef, 1], 
    [ ],
) {
    print "\@\$_ is @$_\n";
    (my ($foo, $bar) = @$_)
        || print "I would die here\n";
    print "\n";
}
[download]

You see, once you actually treat an array as a container of a list, rather than treating it as a list of scalar elements, then all of a sudden it becomes clear what he was testing for. A list with two undefined elements is not an empty list; it is a list with two undefined elements. In real world examples, instead of @$_ one would be using a function call (as the OP eventually demonstrated in his other post), much like the common while(my ($k, $v) = each %hash) { } idiom. This will not abort looping on pairs such as '' => undef because that is not an empty list - it will continue running until, when each reaches the end of the hash, it receives an actual empty list.

Makeshifts last the longest.