NullPointerException On Toast

this is my code:

 case PlaybackStateCompat.STATE_ERROR: {

                        mRadioProgress.setVisibility(View.GONE);
                        mPlayStopButton.setVisibility(View.VISIBLE);
                        mPlayStopButton.setImageResource(R.drawable.player_play);

                        Toast.makeText(MainActivity.this, "Streaming not available", Toast.LENGTH_SHORT).show();

                        break;
                    }

and this is Crashlytics stack trace:

Fatal Exception: java.lang.NullPointerException: Attempt to invoke interface method 'void android.app.INotificationManager.enqueueToast(java.lang.String, android.app.ITransientNotification, int)' on a null object reference
   at android.widget.Toast.show(Toast.java:286)

Code is in MainActivity, which includes a radio player.Is it because the user has already closed MainActivity, making the context invalid? How can I prevent the crash?

Change

Toast.makeText(MainActivity.this, "Streaming not available", Toast.LENGTH_SHORT).show();

to this

Toast.makeText(getApplicationContext(), "Streaming not available", Toast.LENGTH_SHORT).show();