Devel::Cover: uninitialized value warning in 'cover'

As I have described previously, I use Devel::Cover to measure the extent 
to which parts of the Parrot virtual machine's test suite exercises 
certain Perl 5 programs and modules in Parrot's configuration and build 
systems.  Today for the first time I noticed this uninitialized value 
warning, which occurs after the test harness has completed and the 
cover_db has been built, but just before I call 'cover' to generate a 
report or summary:

#####
Reading database from /home/jimk/parrot/coverage/configure-build
Use of uninitialized value $Devel::Cover::Ignore_filenames in regexp 
compilation at 
/usr/local/lib/perl5/site_perl/5.16.0/i686-linux/Devel/Cover/DB.pm line 882.


------------------------------------------ ------ ------ ------ ------ 
------
File                                         stmt   bran   cond    sub 
total
------------------------------------------ ------ ------ ------ ------ 
------
/usr/local/bin/perldoc                      100.0   50.0    n/a  100.0 
  90.9
/usr/local/bin/pod2man                       97.1   50.0   33.3  100.0 
  80.4
...
#####

Here are the relevant sections of Devel::Cover::DB:

#####
  852 sub cover
  853 {
  854     my $self = shift;
...
  880             unless ($digest)
  881             {
  882                 print STDERR "Devel::Cover: Can't find digest for 
$file\n"
  883                     unless $Devel::Cover::Silent ||
  884                            $file =~ $Devel::Cover::Ignore_filenames ||
  885                            ($Devel::Cover::Self_cover &&
  886                             $file =~ q|/Devel/Cover[./]|);
  887                 next;
  888             }
#####

I cannot locate any other reference to $Devel::Cover::Ignore_filenames 
in Devel::Cover::DB.  That variable is listed in 'use vars' in 
Devel::Cover, but Devel::Cover::DB doesn't (directly, at least) import 
Devel::Cover.

Here is the point in the 'cover' executable where it appears 
Devel::Cover::DB::cover() is called:

#####
334     my %f = map { $_ => 1 } (@{$Options->{select}}
335                              ? map glob, @{$Options->{select}}
336                              : $db->cover->items);
#####

I can't find any location within 'cover' where 
$Devel::Cover::Ignore_filenames is set to a defined value.  However, 
when I used a hacked-up version of 'cover' with this:

#####
  20 $Devel::Cover::Ignore_filenames = '';
  21 use Devel::Cover::DB;
#####

... the uninitialized value warning went away.

Can we get a less hackish way of preventing this uninitialized value 
warning?

Thank you very much.
Jim Keenan