It can be resolved by changing constructor like this to retain passed config variable

public function __construct(array $config = null)
{
// Store config values
self::$config = $config;
// Set up params with user defined or default values
self::$workers = $config['workers'] ?? 0;
self::$host = $config['host'] ?? '0.0.0.0';
self::$port = $config['port'] ?? 80;
self::$debug = $config['debug'] ?? false;
self::$logger = $config['logger'] ?? null;
self::$container = $config['container'] ?? null;
.....