public static function formats($format = null, $handler = null)
    {
        if ($format === null) {
            return static::$_formats;
        }
        if ($format === false) {
            return static::$_formats = ['array' => 'Lead\Collection\Collection::toArray'];
        }
        if ($handler === false) {
            unset(static::$_formats[$format]);
            return;
        }
        return static::$_formats[$format] = $handler;
    }