Bug#787608: mrtg-rrd: Warning "defined(%hash/@array) is deprecated" will cause fatal error with Perl 5.22

[Axel Beckert <abe@debian.org>]

Package: mrtg-rrd
Severity: important
Version: 0.7-5
User: debian-perl@lists.debian.org
Usertags: perl-5.22-transition

Dear Maintainer,

On a Debian Jessie installation of mrtg-rrd I've found tons of the
following set of Perl warnings in the Apache error log:

defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 499.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 499.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 499.
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
defined(%hash) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 524.
defined(%hash) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 524.
defined(%hash) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 524.
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 911.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 911.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 911.
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 924.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 924.
defined(@array) is deprecated at /usr/lib/cgi-bin/mrtg-rrd.cgi line 924.
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)
        (Maybe you should just omit the defined()?)

These deprecation warnings will become fatal errors (and hence become RC
severity) when Perl 5.22 (currently in Experimental) hits unstable.

See
https://metacpan.org/pod/distribution/perl/pod/perldelta.pod#defined-array-and-defined-hash-are-now-fatal-errors

(Bug report written on a different system than the one where the bug was
found.)

-- System Information:
Debian Release: 8.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.16.0-4-amd64 (SMP w/4 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)