Error #1009: Cannot access a property or method of a null object reference

1

So, I’m trying to remove an object after it has exceeded set x and y coordinates but i keep getting this error:

Error #1009: Cannot access a property or method of a null object reference.

I used the same code for another object and it worked fine. The error is coming from line 45 of my ship code which is: parent.removeChild(this);

and line 72 of my Level code which is: ships[count].update();

Here is my Level code :
package
{

import flash.display.MovieClip;
import flash.events.Event;
import flash.ui.Mouse;




public class Level extends MovieClip
{


    var ships:Array;
    var bullets:Array;
    public var avatar:Avatar;




    public function Level()
    {


        avatar = new Avatar();
        addChild( avatar );


        avatar.x = mouseX;
        avatar.y = mouseY;






        //addEventListener(Event.ENTER_FRAME, loop);
        ships = new Array  ;
        bullets = new Array  ;
        
        addEventListener(Event.ENTER_FRAME, update);




    }
    function update(e:Event)
    {
        avatar.x = mouseX;
        avatar.y = mouseY;
        Mouse.hide();
        
        
        
        


        if (numChildren<5)
        {




            var s = new Ship();


            addChild(s);




            s.x = Math.random() * stage.stageWidth;
            s.y = -30;
            //s.rotation = Math.random() * 360;
            ships.push(s);


        }
        for (var bcount=0; bcount<bullets.length; bcount++)
        {
            bullets[bcount].update();
            if (bullets[bcount].parent == null)
            {
                bullets.splice(bcount, 1);
                bcount--;
            }
        }
        for (var count = 0; count<ships.length; count++)
        {
            ships[count].update();
            for (bcount=0; bcount<bullets.length; bcount++)
            {
                if (ships[count].hitTestObject(bullets[bcount]))
                {
                    trace ("HIT");
                    removeChild(ships[count]);
                    ships.splice(count, 1);
                    removeChild(bullets[bcount]);
                    bullets.splice(bcount,1);
                    
                    
                }
                
            }
        }
    }
}

}

Here is my ship code:
package
{

import flash.display.Sprite;
import flash.events.Event;
import flash.display.Stage;





public class Ship extends Sprite
{


    private var speed:int;
    var rotateSpeed:Number;
    var size:Number;
    
    
    






    public function Ship()
    {


        speed = 2+Math.random()*5;
        rotateSpeed = 15;
        size = 5
        this.scaleX = Math.random()* size;
        this.scaleY = this.scaleX;
        trace("Made a Ship")
        
    }
    function update()
    {
        this.rotation += rotateSpeed;
        y = y + speed;
        if (x<0 || x >500 || y < 0 || y > 500)
        {
            


            parent.removeChild(this);
        


    }
    
    }
}

}

Thanks in advance