从互联网获取xml文件时为== null

Question

我有以下情况：我需要从Internet获取xml文件，然后从该文件获取歌词。 Here's the url of this xml。这是我编写并应该执行的代码。

private static class NetworkLyricsDownload extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... voids) {

            try {
                URL url = new URL("http://api.chartlyrics.com/apiv1.asmx/SearchLyricDirect?artist=Eminem&song=Lose%20Yourself");
                XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
                factory.setNamespaceAware(false);
                XmlPullParser xmlPullParser = factory.newPullParser();
                xmlPullParser.setInput(getInputStream(url), "UTF-8");
                boolean insideItem = false;
                int eventType = xmlPullParser.getEventType();
                while (eventType!=XmlPullParser.END_DOCUMENT){
                    if (eventType == XmlPullParser.START_TAG){
                        if (xmlPullParser.getName().equalsIgnoreCase("lyric")){
                            insideItem = true;
                            Log.i(getClass().getName(), xmlPullParser.nextText());
                        }
                    }
                    eventType = xmlPullParser.next();
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (XmlPullParserException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }


            return null;
        }

        private InputStream getInputStream(URL url){
            try {
                return url.openConnection().getInputStream();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
    }

但是当我运行该应用程序时，出现以下错误：

E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
    Process: asus.example.com.player, PID: 14458
    java.lang.RuntimeException: An error occurred while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:354)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
        at java.util.concurrent.FutureTask.run(FutureTask.java:271)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)
     Caused by: java.lang.IllegalArgumentException: is == null
        at org.kxml2.io.KXmlParser.setInput(KXmlParser.java:1636)
        at asus.example.com.player.UploadLyricsActivity$NetworkLyricsDownload.doInBackground(UploadLyricsActivity.java:114)
        at asus.example.com.player.UploadLyricsActivity$NetworkLyricsDownload.doInBackground(UploadLyricsActivity.java:86)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245) 
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) 
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) 
        at java.lang.Thread.run(Thread.java:764) 

我在清单文件（<uses-permission android:name="android.permission.INTERNET"/>中具有权限 ），但仍然无济于事。那么，怎么了，我该如何解决？

UPD

这是我的清单文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="asus.example.com.player"
    android:targetSandboxVersion="1">

    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        android:networkSecurityConfig="@xml/network_security_config"
        android:usesCleartextTraffic="true"
        tools:ignore="AllowBackup,GoogleAppIndexingWarning,UnusedAttribute">
        <activity android:name=".SongLyricsActivity"/>
        <activity android:name=".UploadLyricsActivity" />
        <activity
            android:name=".ListOfSongsActivity"
            android:launchMode="singleTask">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".MainActivity" />

        <service
            android:name=".MyService"
            android:enabled="true"
            android:exported="true"
            tools:ignore="ExportedService" />
    </application>

</manifest>