code: public final void setDialogWindowBackground(@Nullable final Bitmap windowBackground) {
          this.dialogWindowBackground =
                  windowBackground != null ? new BitmapDrawable(windowBackground) : null;
          this.dialogWindowBackgroundBitmap = windowBackground;
          this.dialogWindowBackgroundId = -1;
      }
docs: Sets the window background of the preference's dialog.
  
  @param windowBackground
  The window background, which should be set, as an instance of the class {@link
  Bitmap} or null, if no window background should be set