uninitialized value in pattern match

[gilgames]

#!/usr/bin/perl

use warnings;
use strict "refs";
use strict "subs";
use strict "vars";

our $netscape;

$netscape = ($ENV{HTTP_USER_AGENT} =~ /netscape/i ) ? 1 : 0;

################################
The compileing reports an

uninitialized value in pattern match (m//) at a.pl line 10

In the real program I got about 20 similar errors if I use warnings
option. All I want here to check if the string "netscape" matches the
environment variable or not. I use the

our $netscape;

line to avoid the only once error, but if I omit it does not makes any
difference. Also the

use warnings

line is itself is enough to generate the warning.
Could somebody help me, what is wrong and how can I avoid such
messages.

I use perl v5.6.1 for MSWin32-386-Multithread

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