Sending Player to other Script

Hello there,

I want to send the player to another script to set a value on the player using this.

 public JGOGameManager GameManager;
 .
 .
 .
 GameManager.SendPlayerDone (this);

The recieving code looks like this :

 public void SendPlayerDone(JGOPlayer_Physics Player) {
         FinishedPlayers++;
 
         if(FinishedPlayers == 1)
         {
             StartCoroutine (StartFinishCountdown ());
         }
 
         Player.SetPlayerPlace(FinishedPlayers);
 
     }

Unfortunately, my code is not working. I get this error

NullReferenceException: Object reference not set to an instance of an object

How can I send the player himself to the script?

Greetz, ITGeist.