In the given code, what are some common mistakes or errors that could lead to the Singleton class not being properly accessed?

One common mistake that could lead to the Singleton class not being properly accessed is not instantiating the class through the static getInstance method. To ensure the Singleton pattern is correctly implemented, always access the Singleton instance through the static getInstance method to guarantee only one instance of the class is created.

class Singleton {
    private static $instance;

    private function __construct() {
        // private constructor to prevent instantiation
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }
}

// Accessing the Singleton instance
$singleton = Singleton::getInstance();