将图像从Android上传到Google云存储：java.lang.NullPointerException

我正在尝试从我的android客户端应用程序上传一个图像到Google Bucket存储，我使用以下代码

但是，当我尝试发布图像时，会出现以下错误：

java.lang.NullPointerException:尝试调用虚拟方法“void” com.google.api.client.json.jsonggenerator.serialize（java.lang.Object）' 关于空对象引用

代码：

try {
    com.google.api.client.http.javanet.NetHttpTransport httpTransport = new com.google.api.client.http.javanet.NetHttpTransport();

    AssetManager am = PublishView.this.getAssets();
    InputStream inputStream = am.open("key.p12"); //key from service account


    //convert key into class File. from inputstream to file. in an aux class.
    File file = stream2file(inputStream);


    JsonFactory JSON_FACTORY = new JsonFactory() {
        @Override
        public JsonParser createJsonParser(InputStream in) throws IOException {
            return null;
        }

    @Override
    public JsonParser createJsonParser(InputStream in, Charset charset) throws IOException {
        return null;
        }

    @Override
    public JsonParser createJsonParser(String value) throws IOException {
            return null;
        }

    @Override
    public JsonParser createJsonParser(Reader reader) throws IOException {
            return null;
        }

     @Override
     public JsonGenerator createJsonGenerator(OutputStream out, Charset enc) throws IOException {
             return null;
         }

     @Override
     public JsonGenerator createJsonGenerator(Writer writer) throws IOException {
            return null;
         }
};



String STORAGE_SCOPE = "https://www.google.com/analytics/feeds/";



//Google Credentianls


GoogleCredential credential = new GoogleCredential.Builder().setTransport(httpTransport)
                        .setJsonFactory(JSON_FACTORY)
                        .setServiceAccountId("MY_SERVICE_NAME@MY_SERVICE_ACC_ID.iam.gserviceaccount.com")
                        .setServiceAccountScopes(Collections.singleton(STORAGE_SCOPE))
                        .setServiceAccountPrivateKeyFromP12File(file)
                        .build();




String URI = "https://storage.googleapis.com/" + "BUCKET_NAME" + "/" + "test" + ".jpg";
                HttpRequestFactory requestFactory = httpTransport.createRequestFactory(credential);

GenericUrl url = new GenericUrl(URI);


//byte array holds the data, in this case the image i want to upload in bytes.
Resources res = getResources();
Drawable drawable = res.getDrawable(R.mipmap.ic_launcher);
Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
byte[] byteArray = stream.toByteArray();
HttpContent contentsend = new ByteArrayContent("image/jpeg", byteArray);

HttpRequest putRequest = requestFactory.buildPutRequest(url, contentsend);

com.google.api.client.http.HttpResponse response = putRequest.execute();
String content = response.parseAsString();
Log.d("debug", "response is:" + response.getStatusCode());
Log.d("debug", "response content is:" + content);

} catch (Exception ex) {

}

有人能指出我做错了什么吗