App crashes when exiting

[Orijinn]

If we use BackHandler.exitApp() on an app not running in Dev mode, the app crashes:

java.lang.RuntimeException:
at android.app.ActivityThread.performDestroyActivity (ActivityThread.java:4247)
at android.app.ActivityThread.handleDestroyActivity (ActivityThread.java:4265)
at android.app.ActivityThread.-wrap6 (ActivityThread.java)
at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1565)
at android.os.Handler.dispatchMessage (Handler.java:102)
at android.os.Looper.loop (Looper.java:154)
at android.app.ActivityThread.main (ActivityThread.java:6247)
at java.lang.reflect.Method.invoke (Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:762)
Caused by: java.lang.NullPointerException:
at com.telephony.TelephonyModule.stopListener (TelephonyModule.java:106)
at com.telephony.TelephonyModule.onHostDestroy (TelephonyModule.java:511)
at com.facebook.react.bridge.ReactContext.onHostDestroy (ReactContext.java:230)
at com.facebook.react.ReactInstanceManager.moveToBeforeCreateLifecycleState (ReactInstanceManager.java:714)
at com.facebook.react.ReactInstanceManager.onHostDestroy (ReactInstanceManager.java:623)
at com.facebook.react.ReactInstanceManager.onHostDestroy (ReactInstanceManager.java:637)
at com.facebook.react.ReactActivityDelegate.onDestroy (ReactActivityDelegate.java:119)
at com.facebook.react.ReactActivity.onDestroy (ReactActivity.java:72)
at android.app.Activity.performDestroy (Activity.java:6959)
at android.app.Instrumentation.callActivityOnDestroy (Instrumentation.java:1154)
at android.app.ActivityThread.performDestroyActivity (ActivityThread.java:4234)

I've narrowed it down to the TelephonyModule.stopListener(), however I'm not that good in Android to be sure the fix is ok.
That's my suggestion:

@ReactMethod
    public void stopListener() {
        if(telephonyPhoneStateListener != null)
            telephonyManager.listen(telephonyPhoneStateListener,
                PhoneStateListener.LISTEN_NONE);
        telephonyManager = null;
        telephonyPhoneStateListener = null;
    }