Flutter download: failed because it threw an exception/error E/WM-WorkerWrapper( 5787): java.util.concurrent.ExecutionException: java.lang.NoSuchMethodError: No virtual method getContentLengthLong()J in class Ljava/net/HttpURLConnection

In android version 21, when I press the download button, I'm getting the following exception.

```
E/WM-WorkerWrapper( 5787): Work [ id=3ca79a7c-3abc-443b-b896-6a6fec29b9a2, tags={ vn.hunghd.flutterdownloader.DownloadWorker, flutter_download_task } ] failed because it threw an exception/error
E/WM-WorkerWrapper( 5787): java.util.concurrent.ExecutionException: java.lang.NoSuchMethodError: No virtual method getContentLengthLong()J in class Ljava/net/HttpURLConnection; or its super classes (declaration of 'java.net.HttpURLConnection' appears in /system/framework/core-libart.jar)
E/WM-WorkerWrapper( 5787): at androidx.work.impl.utils.futures.AbstractFuture.getDoneValue(AbstractFuture.java:516)
E/WM-WorkerWrapper( 5787): at androidx.work.impl.utils.futures.AbstractFuture.get(AbstractFuture.java:475)
E/WM-WorkerWrapper( 5787): at androidx.work.impl.WorkerWrapper$2.run(WorkerWrapper.java:298)
E/WM-WorkerWrapper( 5787): at androidx.work.impl.utils.SerialExecutor$Task.run(SerialExecutor.java:91)
E/WM-WorkerWrapper( 5787): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
E/WM-WorkerWrapper( 5787): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
E/WM-WorkerWrapper( 5787): at java.lang.Thread.run(Thread.java:818)
E/WM-WorkerWrapper( 5787): Caused by: java.lang.NoSuchMethodError: No virtual method getContentLengthLong()J in class Ljava/net/HttpURLConnection; or its super classes (declaration of 'java.net.HttpURLConnection' appears in /system/framework/core-libart.jar)
E/WM-WorkerWrapper( 5787): at vn.hunghd.flutterdownloader.DownloadWorker.downloadFile(DownloadWorker.java:309)
E/WM-WorkerWrapper( 5787): at vn.hunghd.flutterdownloader.DownloadWorker.doWork(DownloadWorker.java:201)
E/WM-WorkerWrapper( 5787): at androidx.work.Worker$1.run(Worker.java:85)
E/WM-WorkerWrapper( 5787): ... 3 more
```