Action Script 3! Newbie help!!!?

[Santa In Your Panties]

Hi, I'm new to AS3 so I'm sure this is an easy one for you guys. I'm writing a simple shooting style game. When a bullet is fired it uses the bullet class and inside that I am trying to get it to detect a collision with an instance called "black_hole" on the stage, here is the code.

if(this.hitTestObject(black_hole))

Where "this" is the bullet.

Only the error I'm getting is "access of undefined property black_hole". Can anyone help?

Thanks!