function first(callable $closure = null) {
        if($closure === null) {
            if(empty($this->data)) {
                return null;
            }
            
            $keys = \array_keys($this->data);
            return ($this->data[$keys[0]] ?? null);
        }
        
        foreach($this->data as $key => $val) {
            $feed = (bool) $closure($val, $key);
            if($feed) {
                return $val;
            }
        }
        
        return null;
    }