$network_wide argument on plugin activate hook in multisite always empty string?

I’m seeing strange behavior contrary to the WordPress documentation as well as contradicting this WP StackExchange answer regarding the value of the $network_wide argument for plugin activation hooks. Specifically, no matter when/where I test the value of $network_wide, the value is always an empty string. Example code/test case:

<?php
/**
 * A test plugin for the network_wide argument.
 *
 * WordPress plugin header information:
 *
 * * Plugin Name: Test Plugin
 * * Plugin URI: https://example.com/
 * * Description: This plugin tests whether or not the network_wide argument is correctly passed.
 * * Version: 0.1
 * * Author: Meitar <[email protected]>
 * * Author URI: https://maymay.net/
 * * License: GPL-3
 * * License URI: https://www.gnu.org/licenses/gpl-3.0.en.html
 */

function test_plugin_activate($network_wide) {
    var_dump($network_wide);
    exit();
}
register_activation_hook(__FILE__, 'test_plugin_activate');

When activated on a subdomain-based multisite install, this code produces an error:

Plugin could not be activated because it triggered a fatal error.

string(0) ""

My first instinct is to assume I have done something wrong. I am using a VVV multisite development environment and still get this error.

I have searched Core Trac but the only ticket that seems relevant (ticket:14170) seems to have been closed years ago.

Am I missing something obvious or is this a regression?

P.S. I asked this over on StackExchange, too.