protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //Permision Request
        ActivityCompat.requestPermissions(MainActivity.this,
                new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                1);
        initialize();
    }

    //For the Intent to get Folder
    private void initialize() {
        Intent i = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        i.addCategory(Intent.CATEGORY_DEFAULT);
        startActivityForResult(Intent.createChooser(i, "Choose directory"), 9999);
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch(requestCode) {
            case 9999:
                //File myFile = new File(data.getData().toString());
                String path = data.getData().toString();
                //View the path
                Log.i("Test", "Result URI " + path);
                Toast.makeText(getApplicationContext(), "Result URI " +data.getData().toString(), Toast.LENGTH_LONG).show();

                //Creating new File for the directory
                File directory = new File(path);
                File[] files = directory.listFiles();

                Log.d("Files", "Size: "+ files.length);
                for (int i = 0; i < files.length; i++)
                {
                    //Show the name of the files in the directory
                    Log.d("Files", "FileName:" + files[i].getName());
                }

                break;
        }
    }

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

Caused by: java.lang.NullPointerException: Attempt to get length of null array
                                                                                  at cu.edu.cujae.citi.folderpicker.MainActivity.workWithFile(MainActivity.java:59)
                                                                                  at cu.edu.cujae.citi.folderpicker.MainActivity.onActivityResult(MainActivity.java:49)
                                                                                  at android.app.Activity.dispatchActivityResult(Activity.java:6932)
                                                                                  at android.app.ActivityThread.deliverResults(ActivityThread.java:4085)
                                                                                  at android.app.ActivityThread.handleSendResult(ActivityThread.java:4132)
                                                                                  at android.app.ActivityThread.-wrap20(ActivityThread.java)
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1533)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                  at android.os.Looper.loop(Looper.java:154)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)