我正在为一个flutter应用程序构建一个配置文件页面，用户从他们的图库上传一张图片，然后图片被上传到FirebaseStorage。我遇到了一个问题，我收到了一个CastError，这是基于对空值使用空值检查操作符。问题变量是imageFile，但我已经使用If语句进行了检查，但我还是收到了这个错误。
下面是我的代码：

String name = '';
  String email = '';
  String? image = '';
  File? imageFile;
  String? imageUrl;
  String? userNameInput = '';

  //Upload image to Firebase
  Future<String?> _uploadImageToFirebase() async {
    if (imageFile == null) {
      Fluttertoast.showToast(msg: 'Please upload an image');
    }
**//This is where I'm getting the CastError**
    String fileName = Path.basename(imageFile!.path);

    var reference =
        FirebaseStorage.instance.ref().child('profileImages/$fileName');
    UploadTask uploadTask = reference.putFile(imageFile!);
    TaskSnapshot taskSnapshot = await uploadTask.whenComplete(() => null);
    await taskSnapshot.ref.getDownloadURL().then((value) {
      imageUrl = value;
    }).catchError((e) {
      Fluttertoast.showToast(msg: e.toString());
    });

    FirebaseFirestore.instance
        .collection('users')
        .doc(FirebaseAuth.instance.currentUser!.uid)
        .set({'userImage': imageUrl});
    return imageUrl;
  }