Update NetworkServer.cs

[J0NY97]

No description provided.

[MrGadget1024]

No description of the issue provided, but conn should never be null there. The only callers have a good connection to pass.
If you're calling that from your code, you're responsible for passing a good connection.
Maybe you should be using NetworkServer.RemovePlayerForConnection instead?

[J0NY97]

It seems like 'conn' would be 'null' if one calls 'NetworkManager.StopHost()' in 'NetworkManager.OnClientDisconnect()'.

[MrGadget1024]

It seems like 'conn' would be 'null' if one calls 'NetworkManager.StopHost()' in 'NetworkManager.OnClientDisconnect()'.

You definitely shouldn't be doing that...Mirror is already in that process at that point.

[J0NY97]

Probably not, but you gotta do whatchu you gotta do.
My 'fix' would make the program run perfectly normal even if you did that.
Otherwise it just gives a NullReferenceException.