public static function unregisterSource($name)
    {
        Validate::isString($name, 'name');
        Validate::notNullOrEmpty($name, 'name');

        self::_init();

        $sourceCallback = Utilities::tryGetValue(self::$_sources, $name);

        if (!is_null($sourceCallback)) {
            unset(self::$_sources[$name]);
        }

        return $sourceCallback;
    }