getBotUserId() returns NULL

[bohemianoid]

When I call the getBotUserId() function, I do not get back the bot user ID but NULL.

Reproduction steps

<?php

use BotMan\BotMan\BotMan;
use BotMan\BotMan\BotManFactory;
use BotMan\BotMan\Drivers\DriverManager;

require __DIR__ . '/../vendor/autoload.php';
require __DIR__ . '/../source/config.php';

DriverManager::loadDriver(\BotMan\Drivers\Slack\SlackDriver::class);

$botman = BotManFactory::create($config);

$botman->loadDriver('Slack');
$botUserId = $botman->getDriver()->getBotUserId();

echo $botUserId;
echo gettype($botUserId);

---

PHP: 7.1.33
Botman: 2.5.0
Slack-Driver: 2.2.0

[hani-borsen]

I think you need this permission:
https://api.slack.com/scopes/users:read