protected function loadManifest()
    {
        if (!is_null($this->manifest)) {
            return;
        }

        if (file_exists($this->manifestPath)) {
            try {
                $this->manifest = $this->files->getRequire($this->manifestPath);

                if (!is_array($this->manifest)) {
                    $this->manifest = [];
                }
            } catch (Exception $ex) {
                $this->manifest = [];
            }
        }
        else {
            $this->manifest = [];
        }
    }