code: public void setFillWithGradient(final boolean FILL_WITH_GRADIENT) {
          if (null == fillWithGradient) {
              _fillWithGradient = FILL_WITH_GRADIENT;
              fireTileEvent(REDRAW_EVENT);
          } else {
              fillWithGradient.set(FILL_WITH_GRADIENT);
          }
      }
docs: Defines the usage of a gradient defined by gradientStops to fill the area
  in the SmoothAreaTileSkin
  @param FILL_WITH_GRADIENT