@Happycrusher764, please refer to my Scrolling Tutorial scenario -- and next time, do not interrupt a discussion with something that is not relevant to that discussion (in other words, start a new one of your own).
There are a few occasions in your RobotWorld class where null is being used as an argument in a call to create a new GreenfootImage object, which no longer works (since the change from java.util.Color to greenfoot.Color). Replace them with actual (greenfoot.) Color objects. Background color "null"s can be replaced with "new Color(0, 0, 0, 0)".