reading file producing NullPointerException

Question

I'm trying to open up file selector in my Android Program, like this:

Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("*/*");
        intent.addCategory(Intent.CATEGORY_OPENABLE);

Now inside onActivityResult, I'm doing:

Uri uri = data.getData();
                    Log.d(TAG, "File Uri: " + uri.toString());
                    path = MainActivity.getPath(this, uri);
                    Log.d(TAG, "File Path: " + path);
                    try {
                        //readFile(uri.toString())
                        readFile(path);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }

And inside read file I'm just trying to read it's content, which is giving me nullPointerException.

    private static void readFile(String path) throws Exception {
        Log.d(TAG,"inside readFile -->> "+path);
        String data=MainActivity.getStringFromFile(path);
        Log.d(TAG,"data "+data);
    }



    public static String convertStreamToString(InputStream is) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append("\n");
        }
        reader.close();
        return sb.toString();
    }

    public static String getStringFromFile (String filePath) throws Exception {
        File fl = new File(filePath);
        FileInputStream fin = new FileInputStream(fl);
        String ret = convertStreamToString(fin);
        fin.close();
        return ret;
    }

How can I resolve this ?

Even I have taked external storage permission, although I don't have one.

Path looks something like this : /storage/emulated/0/CodeRead/springboot-react-chatroom-master/springboot-react-chatroom-master/README.md

And the URI : content://com.mi.android.globalFileexplorer.myprovider/external_files/CodeRead/springboot-react-chatroom-master/springboot-react-chatroom-master/README.md

Trace :

2020-04-01 17:26:00.502 22327-22327/com.org.orgcodereader W/System.err:     at com.org.orgcodereader.activity.MainActivity.getStringFromFile(MainActivity.java:165)
2020-04-01 17:26:00.502 22327-22327/com.org.orgcodereader W/System.err:     at com.org.orgcodereader.activity.MainActivity.readFile(MainActivity.java:147)
2020-04-01 17:26:00.502 22327-22327/com.org.orgcodereader W/System.err:     at com.org.orgcodereader.activity.MainActivity.onActivityResult(MainActivity.java:135)
2020-04-01 17:26:00.503 22327-22327/com.org.orgcodereader W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6864)
2020-04-01 17:26:00.503 22327-22327/com.org.orgcodereader W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)

I noticed sometimes MainActivity.getStringFromFile(path); is producing null, so this happens. And there is special reason behind that I guess, if I select on recent or other options, but if I select FileManager it works fine.

When I select other method the URI looks something just like this :

content://com.android.externalstorage.documents/document/primary%3APictures%2FInstagram%2FIMG_20200305_214854_891.jpg