在与 Parse 服务器交谈时（在 iOS 上使用 Swift），为什么 PFFileObject 一直返回 nil？

Question

为什么 PFFileObject 总是给我一个像Foundation._GenericObjCError.nilError这样的错误，如果我使用PFFileObject(name:data:)创建一个文件对象，我会得到nil 。

我的代码看起来像：

func uploadImageFileToParseServer(image: UIImage, uid: String) {
        guard let imageData = image.pngData() else {
            UILogger.error("Null imageData")
            return
        }
        UILogger.log("creating imageFile using \(uid) and \(imageData) under name \(uid)-img.png")
        
        let unwrappedImageFile = try? PFFileObject(name: "\(uid)-img.png", data: imageData, contentType: "image/png")

        unwrappedImageFile?.saveInBackground { (result, error) in
            if let error = error{
                UILogger.error("\(String(describing: error))")
            } else {
                let query = PFQuery(className: "User")
                UILogger.log("Saving to User with uid \(uid)")
                query.whereKey("objectId", equalTo: uid)
                query.findObjectsInBackground(block: { (objects, error) in
                    if let user = objects {
                        for object in user {
                            UILogger.log("User \(uid) found. Updating his/her avatar column now")
                            object["avatar"] = unwrappedImageFile
                            object.saveInBackground { isSuccessful, error in
                                if !isSuccessful {
                                    UILogger.error("Error in updating User - \(error.debugDescription)")
                                }
                            }
                        }
                    }
                })
            }
        }
    }