code: public Bbox buffer(double range) {
  		if (range > 0) {
  			double r2 = range * 2;
  			return new Bbox(x - range, y - range, width + r2, height + r2);
  		}
  		return null;
  	}
docs: Return a new bounding box that has increased in size by adding a range to this bounding box.
  
  @param range Must be a positive number, otherwise null will be returned.
  @return new buffered bounding box