function enrol_get_shared_courses($user1, $user2, $preloadcontexts = false, $checkexistsonly = false) {
global $DB, $CFG;
- $user1 = !empty($user1->id) ? $user1->id : $user1;
- $user2 = !empty($user2->id) ? $user2->id : $user2;
+ $user1 = isset($user1->id) ? $user1->id : $user1;
+ $user2 = isset($user2->id) ? $user2->id : $user2;
if (empty($user1) or empty($user2)) {
return false;