Why would one put `#! /usr/bin/false` in a Perl Module?

Why would one put `#! /usr/bin/false` in a Perl Module?

I was looking at the source code for the CPAN Perl module
Digest::MD5::Perl and noticed that it has the she bang #! /usr/bin/false.
Here's the first few lines of Digest/Perl/MD5.pm ...
#! /usr/bin/false
#
# $Id: MD5.pm,v 1.19 2004/02/14 02:25:32 lackas Exp $
#
package Digest::Perl::MD5;
use strict;
use integer;
use Exporter;
use vars qw($VERSION @ISA @EXPORTER @EXPORT_OK);
... why would the author of Digest::Perl::MD5 use #! /usr/bin/false? And
what if my system does not have /usr/bin/false but has /bin/false instead?