WC_Order::maybe_set_user_billing_email PHP Method

    protected function maybe_set_user_billing_email()
    {
        if (!$this->get_billing_email() && ($user = $this->get_user())) {
            try {
                $this->set_billing_email($user->user_email);
            } catch (WC_Data_Exception $e) {
                unset($e);
            }
        }
    }