Getting a / when regex should produce nothing

When I run this first time, with no values from form, I get 
$article_file being a / when it should be nothing. I just can't see the 
error. I have tried variations with \w and dash at beginning and end, 
but no go.

Debug shows blank at A, / at B

#!/usr/bin/perl

$VERSION = 1.0.0;

use warnings;
no warnings 'uninitialized';
use strict;

#use Apache::Constants qw(:common);
use Apache::Request();
#use Apache::Cookie();
use MyPerl::Articulator qw(get_template print_template print_text 
submit_changes backup_server see_html template_form load_template);

our $debug = 1;

delete $ENV{PATH};
my $r = Apache->request;
my $q = Apache::Request->new($r, POST_MAX => 1000000, DISABLE_UPLOADS => 1);
my $site_url = "www.example.com";
my $site_directory = "/var/www/htdocs/users/example.com";
my $site_name = "Example!";
my $secure = 1;
my $article_directory = "articles";
undef my $error;
undef my $article_title;
undef my $article_backup_file;
undef my $article_file;
$article_file = $q->param("articlefilename");
if ($debug) { $error .= qq{<p>$article_file</p>};}
$article_file =~ m/^([a-zA-Z0-9_-]*\.html)$/;
$article_file = $1;
if ($debug) { $error .= qq{<p>$article_file</p>};}
$article_backup_file = $article_file;
$article_backup_file =~ s/\.html$/_backup.html/;
undef my $body;

Thanks
Chris Bennett

-- 
A human being should be able to change a diaper, plan an invasion,
butcher a hog, conn a ship, design a building, write a sonnet, balance
accounts, build a wall, set a bone, comfort the dying, take orders,
give orders, cooperate, act alone, solve equations, analyze a new
problem, pitch manure, program a computer, cook a tasty meal, fight
efficiently, die gallantly. Specialization is for insects.
    -- Robert Heinlein