Notice: Undefined property: stdClass::$defaulthomepage in /var/www/html/moodle/index.php

I had upgraded my Moodle site from 1.9 to 2.2.2+.
After upgrading the site I accessed front page, then I got a notice message "Notice: Undefined property: stdClass::$defaulthomepage in /var/www/html/moodle/index.php" on the top of the front page.
I didn't use mymoodle on 1.9.

So, if I change "Debug messages" from NORMAL to NONE, I'll not get the notice message. But now I'm debugging my Moodle2.2.2+ site.

I modified moodle/index.php as follows for avoiding the notice;

require_once('config.php');
require_once($CFG->dirroot .'/course/lib.php');
require_once($CFG->libdir .'/filelib.php');

redirect_if_major_upgrade_required();

$urlparams = array();
// (Shirai): add from here
// if (empty($CFG->defaulthomepage)) $CFG->defaulthomepage = NULL;
// (Shirai): add to here
if ($CFG->defaulthomepage == HOMEPAGE_MY && optional_param('redirect', 1, PARAM_BOOL) === 0)

$PAGE->set_url('/', $urlparams);
$PAGE->set_course($SITE);

This modification is not fundamental countermeasure.
Why $CFG->defaulthomepage does not assigning any value (including NULL)?
Which process of migrating is assign valid value of $CFG->defaulthomepage?