(http://moodle.org/bugs/bug.php?op=show&bugid=5709&)
Merged from MOODLE_16_STABLE
//Call the form, depending the step we are
if (!$launch) {
// if we're at the start, clear the cache of prefs
- unset($SESSION->backupprefs[$course->id]);
+ if (isset($SESSION->backupprefs[$course->id])) {
+ unset($SESSION->backupprefs[$course->id]);
+ }
include_once("backup_form.html");
} else if ($launch == "check") {
include_once("backup_check.html");