Ошибка в Yii2 Undefined offset: 6, как решить?

Question

[Ghost2692]

Возникает такая ошибка Undefined offset: 6 в ряду

$item = $changeOnUnsubscribed->selected_checkbox[$i];

Как ее решить?

$changeOnUnsubscribed = new ContactList();
        if ($changeOnUnsubscribed->load(Yii::$app->request->post())) {
            $contactId = ContactList::find()->where(['contact_id' => $id])->all();
            foreach ($contactId as $id) {
                $count = count($changeOnUnsubscribed->selected_checkbox);
                for ($i = 0; $i <= $count; $i++) {
                    $item = $changeOnUnsubscribed->selected_checkbox[$i];
                    if ($item != 0) {
                        if ($item == $id->id) {
                            $changeOnUnsubscribed->status = 0;
                            $changeOnUnsubscribed->save();
                        }
                    }
                }
            }
        }