PHP NotORM + MYSQL

function register()
{
    $_USER = $this->loadModel('UserModel');

    $array = array(
        "id" => $this->getRN('USER'),
        "fullname" => $_POST['record']['fullname'],
        "nickname" => $_POST['record']['nickname'],
        "email" => $_POST['record']['email'],
        "phone" => '',
        "address" => '',
        "status" => 'Nonactive',
        "usergroup_id" => '4',
        "password" => $_POST['record']['password']
    );

    $_USER->addUser($array);

    die();
}

public function addUser($array = null)
{
    $this->notorm()->user()->insert($array);
}

hello, i need to check in my function 'register', if email is already exits. if yes return message that he can not register to the system, can anyone please can help me to fix it?