Creating a xml file to store data local c# and read data from that created file

I want to store data that i get from a url into a xml file and show that data when there is no internet.

I have this:

 async Task CreateSaveFile()
    {
        // Create document
        XDocument xmlDocument = new XDocument(new XDeclaration("1.0", "utf-8", "yes"),
            new XElement("Objects", from test in TestList
                                  select new XElement("test",
                                      new XElement("name", test.Name),
                                      new XElement("number", test.Number))));

        // Storage Folder
        StorageFolder folder = Windows.Storage.ApplicationData.Current.LocalFolder;
        string fileName = "test.xml";
        StorageFile file = await folder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
        Stream stream = await file.OpenStreamForWriteAsync();

        // Write file
        xmlDocument.Save(stream);
        stream.Flush();
    }

And this method to get the data from the created test.xml into a list:

 private List<Test> testList = new List<Test>();
 async Task<List<Test>> getTestList()
    {
        StorageFolder folder = Windows.Storage.ApplicationData.Current.LocalFolder;
        IReadOnlyList<StorageFile> files = await folder.GetFilesAsync();


        foreach (StorageFile file in files)
        {
        // Get xml files
        XDocument xmlFile = XDocument.Load(file.Path);

        // Get TestObjects
        testList = (from element in xmlFile.Root.Descendants("test")
                       select new Player(
                           element.Element("name").Value,
                           element.Element("number").Value)).ToList<Test>();

        }

        return testList;
    }

I get this error An unhandled exception of type 'System.Reflection.TargetInvocationException' occurred in System.Windows.ni.dll‏