The ping in scoreboard is always 0

I did this to can show the ping in the scoreboard for each player, but for all players the ping is 0:

And i get this warning: Trying to send command for object without authority.

Code (CSharp):

1.     [SyncVar]
2.     public int playerPing = 0;
3.  
4.     void Update()
5.     {
6.         CmdShowPing(); //Warning Here
7.     }
8.  
9.  
10.     [Command]
11.     private void CmdShowPing()
12.     {
13.         if (NetworkManager.singleton != null)
14.         {
15.             playerPing = NetworkManager.singleton.client.GetRTT();
16.         }
17.     }

 

Only call the command if you have authority. (if hasAuthority)

 

ok, the warning is fixed, but the ping is always 0:

 

GetRTT is null on the server. You need to get the client connection that you want to measure


EDIT:
I meant the Client on the NetManager is null. Atleast So I think