actor not in world

public class Rocket extends Actor
{
    private int xdistance=0,ydistance=0; 
    boolean fire = true; 
    private boolean toRemove=false;
     
    public void addedToWorld(World MyWorld) 
    { 
       xdistance=getX(); 
       ydistance=getY(); 
    } 
     
    public void move() 
    { 
      double rx=xdistance-getX(); 
      double ry=ydistance-getY(); 
      double r=Math.sqrt(rx*rx+ry*ry); 
      int b=5; 
      int posx=0,posy=0;
      if(r>b)  
      {  
        posx=(int)(getX()+b*rx/r);  
        posy=(int)(getY()+b*ry/r);
        } else{  
            posx=xdistance; 
            posy=ydistance; 
        } 
        setLocation(posx,posy); 
    } 
    
   
    public void act() 
    {
      if(Greenfoot.mouseMoved(null))  
      { 
          MouseInfo mouse=Greenfoot.getMouseInfo(); 
          xdistance=mouse.getX(); 
          ydistance=mouse.getY(); 
        } 
       move(); 
       fireLasars(); 
       gameOver(); 
        
    }
    public void fireLasars()  
    {  
        if(Greenfoot.isKeyDown("a") && fire == true ) 
        { 
            getWorld().addObject(new Lasars(),getX() - 30,getY());  
            fire = false; 
        } 
        else if (!Greenfoot.isKeyDown("a")) 
        { 
            fire = true; 
        }
}   
public void gameOver() 
{ 
   Actor meteor = getOneIntersectingObject(Meteors.class); 
        if(meteor != null) 
        { 
        getWorld().removeObject(this);  
        Greenfoot.stop(); 
         }   
        if(this.isAtEdge() == true)
        {   
            World world;
            world = getWorld();
            getWorld().removeObject(this);  
            Greenfoot.stop(); 
        }
         
         
 }