Why can't the application open the file for reading?

Question

Android

There is an application that, when you click on the "Save" button, writes two values ​​\u200b\u200binto a file.
When you click on the "Read" button, it should read the file and select these values ​​from the line.
When saving, there are no errors, and a message is displayed in the console that the save was successful.
But when reading, the application crashes on line 1.

Save/read code

private String M_PREFS = "Lab7";
private String FILE_NAME = "font_settings2";

private String loadViewSettings() {
    String str = "";
    try {
        FileInputStream file = openFileInput(FILE_NAME); 
        BufferedReader br = new BufferedReader(new InputStreamReader(file));  // 1 Тут происходит краш
        while ((str = br.readLine()) != null) {
            Log.d(M_PREFS, str);
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return str;
}

private void saveViewSettings() {
    try {
        getApplicationContext().deleteFile(FILE_NAME);
        BufferedWriter bw = new BufferedWriter(
                new OutputStreamWriter(openFileOutput(FILE_NAME, MODE_PRIVATE))
        );
        int color, sise;
        switch (this.color) {
            case Color.RED:
                color = 0;
                break;

            case Color.BLUE:
                color = 1;
                break;

            default:
                color = 2;
        }

        switch (this.size) {
            case 33:
                size = 0;
                break;

            case 23:
                size = 1;
                break;

            default:
                size = 2;
        }
        bw.write(String.format("%d%d", color, size));
        bw.close();
        Log.d(M_PREFS, "Файл записан");
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Mistake

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: ru.knastu.tempfct.livenlab7, PID: 9579
    java.lang.NullPointerException: Attempt to invoke virtual method 'char[] java.lang.String.toCharArray()' on a null object reference
        at ru.knastu.tempfct.livenlab7.MainActivity.onClick(MainActivity.java:214)
        at android.view.View.performClick(View.java:6261)
        at android.widget.TextView.performClick(TextView.java:11185)
        at android.view.View$PerformClick.run(View.java:23752)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6776)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)

When testing, first I save, then I read.
What am I doing wrong?
UPD: Updated the crash
site UPD2: String.toCharArray()' on a null object - the result of the fact that after line 1 the function crashes and returns null instead of the data from the file.

Answer 1

In the MainActivity.onClick method, you call java.lang.String.toCharArray()
by reference without a java.lang.NullPointerException object