Not able to get files from any Android folder

I am new in android and was trying to test something. I have this simple app, where I just want to read files from any android folder. Till now, I just checked how the paths are there which I came to know from the following

context.getExternalFilesDir(null);

&

Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM)

The paths obtained are like

/storage/emulated/0/ then rest of the folders

I have done everything, asked for permission in the manifest file, and in the app too. I check that even though the permission is granted and folder path is also correct but the File.listFiles() is givingme null pointer exception.

Please take a look at the code below:

Permission in manfest file

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

Code to get permission and try checking the files

 if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
        ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},101);
        Toast.makeText(getApplicationContext(),
                "No permission yet",
                Toast.LENGTH_SHORT).show();
    }
    else{
        Toast.makeText(getApplicationContext(),
                "Permission already granted",
                Toast.LENGTH_SHORT).show();
       
        File dcimPath = new File("/storage/emulated/0/bluetooth"); //This path is correct
        
        File[] files = dcimPath.listFiles(); // gives null pointer exception
        Log.i("files length ",files.length+"");
    }

     @Override
     public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if(requestCode == 101){
        if(grantResults[0] == PackageManager.PERMISSION_GRANTED){
            Toast.makeText(getApplicationContext(),
                    "Permission granted",
                    Toast.LENGTH_SHORT).show();
            File dcimPath = new File("/storage/emulated/0/bluetooth/"); 

            File[] files = dcimPath.listFiles(); //gives error
            Log.i("files length ",files.length+"");
        }
        else{
            Toast.makeText(getApplicationContext(),
                    "Permission denied",
                    Toast.LENGTH_SHORT).show();
        }
    }
}

ERROR

 Caused by: java.lang.NullPointerException: Attempt to get length of null array