Automatically change user role after completed orders in WooCommerce

I’m using code that gives the user a new role after three orders.

The default user role is “Customer” and I have created an additional role “Regular Customer”.

/* Create a new role */
add_action('init', 'luckydoll_add_custom_user_role');
function luckydoll_add_custom_user_role() {
    add_role('regular_customer', __('Regular Customer', 'woocommerce'), array(
        'read' => true,
        'create_posts' => false,
    ));
}

/* Change user role after three orders */
function total_completed_orders( $the_user_id ) {
    global $wpdb;
    
    $count = $wpdb->get_var(
        // phpcs:disable WordPress.DB.PreparedSQL.NotPrepared
        "SELECT COUNT(*)
        FROM $wpdb->posts as posts
        LEFT JOIN {$wpdb->postmeta} AS meta ON posts.ID = meta.post_id
        WHERE   meta.meta_key = '_customer_user'
        AND     posts.post_type = 'shop_order'
        AND     posts.post_status = 'wc-completed'
        AND     meta_value = '" . esc_sql( $the_user_id ) . "'"
        // phpcs:enable
    );

    return $count;
}

add_action( 'woocommerce_order_status_completed', 'action_woocommerce_order_status_completed', 10, 1 );
function action_woocommerce_order_status_completed( $order_id ) {
    
    // User role in which the customer role must be changed
    $premium_user_role = 'regular_customer';
    
    // Spending min cash in one order
    $min_in_one_order = 400;
    
    // Change role after x completed orders
    $change_role_after_x_completed_orders = 3;
    
    $flag = false;
    
    // Get an instance of the WC_Order object
    $order = wc_get_order( $order_id );
    
    // Is a order
    if( is_a( $order, 'WC_Order' ) ) {
        // Get user ID or $order->get_customer_id();
        $user_id = $order->get_user_id();
        
        // Retrieve user meta field for a user. 
        $is_premium = get_user_meta( $user_id, '_customer_is_premium_member', true );
        
        // Is NOT a premium member
        if ( $is_premium != 1 ) {
            // Count total completed orders
            $total_completed_orders = total_completed_orders( $user_id );
            
            // Total completed orders greater than or equal to change role after x completed orders
            if ( $total_completed_orders >= $change_role_after_x_completed_orders ) {
                $flag = true;
            } else {
                // Get current order total
                $order_total = $order->get_total();
                
                // Order total greater than or equal to minimum in one order
                if ( $order_total >= $min_in_one_order ) {
                    $flag = true;
                }
            }
            
            // True, at least 1 condition has been met
            if ( $flag ) {
                // Get the user object
                $user = get_userdata( $user_id );

                // Get all the user roles as an array.
                $user_roles = $user->roles;
                
                // User role contains 'customer'
                if ( in_array( 'customer', $user_roles ) ) {
                    // Remove customer role
                    $user->remove_role( 'customer' );
                    
                    // Add premium role
                    $user->add_role( $premium_user_role );
                    
                    // Update user meta field based on user ID, set true
                    update_user_meta( $user_id, '_customer_is_premium_member', 1 );
                }
            }
        }
    }
}

When a registered user places three orders, their role automatically changes.

But if a guest makes an order and the manager sets his order to the “Done” status, a critical error appears.

line 347: $user_roles = $user->roles;
line 350: if ( in_array( 'customer', $user_roles ) ) {

I can disable guest checkout. On the other hand, I can’t force guests to register on the site if they don’t want to.

How can this error be fixed? Is it possible to exclude guests from this custom code?