Help with respawn

Hey guys i just started my "own" small Unity project. The problem i have now is, that is used a variety of different tutorials and stuff and now i got a problem with the respawn system. I made the scripts for with with this tutorial: https://www.youtube.com/watch?v=ndYd4S7UkAU I wrote and attached the scripts exactly the same as in the video, but when i want to try it i get this error: NullReferenceException: Object reference not set to an instance of an object Levelmanager.respawn () (at Assets/script/Levelmanager.cs:29) killplayer.OnTriggerEnter2D (UnityEngine.Collider2D other) (at Assets/script/killplayer.cs:25) When my player hits the spikes i get the notification from the Debug.Log but the game stops. here my scipts http://imgur.com/a/7uTFj