离线模式Firebase存储

Question

我正在创建此功能来设置我的映像，该映像存储在firebase存储器中并且可以正常工作，但是当模拟器离线时，它不会遍历我的默认本地保存映像

func downloadImageFromFirebase(_ imageNameOnFireBase: String, _ defaultLocalImageName: String, _ imageToBeReplaced: UIImageView) {
    let storage = Storage.storage()
    let reference: StorageReference = storage.reference().child(imageNameOnFireBase)
    let defaultImage = UIImage(named: defaultLocalImageName)
    reference.downloadURL { url , error in
        if error != nil {
            imageToBeReplaced.image = defaultImage
        }else{
            if let url = url {
                do {
                    let data = try Data.init(contentsOf: url)
                    imageToBeReplaced.image = UIImage(data: data)!
                } catch {
                    print("Error fetching URL")
                    imageToBeReplaced.image = defaultImage
                }
            } else {
                imageToBeReplaced.image = defaultImage
            }
        }
    }
}

如果模拟器或设备处于离线模式，我如何使该功能获取本地图像？