WP/WC missing argument in WooCommerce Function

You missed one parameter. Try this.

do_action( 'wp_login', $user->user_login, $user );

Source: https://developer.wordpress.org/reference/hooks/wp_login/

if (!is_user_logged_in()) {

    //determine WordPress user account to impersonate
    $user_login = 'guest';

    //get user ID
    $user = get_userdatabylogin($user_login); // below WP 3.3.0

    //$user =  get_user_by('login', $user_login); above or equals WP 3.3.0

    $user_id = $user->ID;

    //login
    wp_set_current_user($user_id, $user_login);
    wp_set_auth_cookie($user_id);
    do_action('wp_login', $user_login);
}

There is a hook in WooCommerce like this.

add_action( 'wp_login', 'wc_maybe_store_user_agent', 10, 2 );

The "wc_maybe_store_user_agent" expects 2 parameter. If the user ID is not set, it will show the error you mentioned. Test my snippet above

Function is at line 1516 in plugins/woocommerce/includes/wc-core-functions.php

function wc_maybe_store_user_agent( $user_login, $user ) {
    if ( 'yes' === get_option( 'woocommerce_allow_tracking', 'no' ) && user_can( $user, 'manage_woocommerce' ) ) {
        $admin_user_agents   = array_filter( (array) get_option( 'woocommerce_tracker_ua', array() ) );
        $admin_user_agents[] = wc_get_user_agent();
        update_option( 'woocommerce_tracker_ua', array_unique( $admin_user_agents ) );
    }
}
add_action( 'wp_login', 'wc_maybe_store_user_agent', 10, 2 );