Flutter 所需引用Firebase处不存在任何对象

我是Firebase的新手，目前正在使用Firebase存储，并且已经成功上传了我的文件(问题不在这里).

问题在于获取上载文件的下载链接.

代码

    Reference ref = FirebaseStorage.instance.ref('userImages/${FirebaseAuth.instance.currentUser?.uid}');

    if(image != null){
      ref = ref.child(Uri.file(image!.path).pathSegments.last);
      var link = await ref.putFile(image!).snapshot.ref.getDownloadURL(); //this line generates error
      // or even link = await ref.getDownloadURL();
      ref = ref.parent!;
    }
    if(cover !=null){
      ref = ref.child(Uri.file(cover!.path).pathSegments.last);
     var link = await ref.putFile(cover!).snapshot.ref.getDownloadURL();
      ref = ref.root;

    }

E/StorageException(16989): StorageException has occurred.
E/StorageException(16989): Object does not exist at location.
E/StorageException(16989):  代码: -13010 HttpResult: 404
E/StorageException(16989): {  "error": {    "code": 404,    "message": "Not Found."  }}
E/StorageException(16989): java.io.IOException: {  "error": {    "code": 404,    "message": "Not Found."  }}

我认为推荐信指向了错误的地方，谢谢.