Why do object reference become null after passing it as argument to a class constructor? but it wasnt null before

I tried spot the problem using a debugger but i failed. All I understood is where the exception occur: when trying to use the reference of the object of type Image (stored in the variable image) in an instance of the object of type Landmark; here is my code:

public class Viewer implements MouseMotionListener, ActionListener {
    //I put a  break point here but all is right: image is not a null pointer here
    MarvinImage image = loadImage("imag.png"); 
    ....
    public class ActionHandler implements ActionListener, MouseListener {
        public void actionPerformed(ActionEvent event) {
            Landmarks l = new Landmarks(image);
        }
    }
}

public class Landmarks() {

    public Landmarks(MarvinImage image) {
        //when i try to use image here the compiler says java.langNullPointerExeption
    }
}