Hello,Thank you in advance for making your code public.
The exception comes from the drawBitmap method under the MainSurface class!

 @Override
 public void drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint) {	
 this.paint.getGraphics().drawImage(bitmap.getImage(),((JMatrix)matrix).trans, null);
 }

When executing bitmap.getImage (), NullPointerException is caused because the bitmap is null. You should add the if module! Thank you for reading