protected function _cleanFilesStack()
    {
        if (true===$this->isCleaned_files_stack) {
            return;
        }

        $new_stack = array();
        foreach ($this->files_stack as $_file) {
            if (is_object($_file) && ($_file instanceof \SplFileInfo)) {
                $new_stack[] = $_file;
            } elseif (is_string($_file) && @file_exists($_file)) {
                $new_stack[] = new \SplFileInfo($_file);
            } elseif (false===$this->silent) {
                throw new \RuntimeException(
                    sprintf('[Compressor] Source to process "%s" not found!', $_file)
                );
            }
        }
        $this->files_stack = $new_stack;
        $this->isCleaned_files_stack = true;
    }