public function has(?string $key) : bool
    {
        return $key === null ? false : isset($this->themes[$key]);
    }
public function has(?string $key) : bool
    {
        return $key === null ? false : isset($this->themes[$key]);
    }
public function has ( ? string $ key ) : bool { return $ key === null ? false : isset ( $ this -> themes [ $ key ] ) ; }
Check if theme exists

@param string $key
@return bool
Check if theme exists