My guess would be that findByName is not returning what you think it is. You may have another item in your hierarchy that is being found first, which does not have a rigid body component. Set a breakpoint and inspect this.arrow.
Wow cool, i have changed the rigidbody to kinematic and moved the arrow entity just under my terrain entity and when function is fired the terrain disapared. Magic Arrow LOL
Edit: correction, it doesn’t disapear…it get fired