multiple bugfixes

wizard-server/src/main/java/eu/jonahbauer/wizard/server/debug/DebugSession.java

@@ -61,9 +61,12 @@ public class DebugSession extends Session {
     protected void startGame() {}
 
     public void close() {
-        for (var player : getPlayers().values()) {
+        for (var sessionPlayer : getPlayers().values()) {
             try {
-                player.getPlayer().disconnect();
+                var player = sessionPlayer.getPlayer();
+                if (player != null) {
+                    player.disconnect();
+                }
             } catch (IOException ignored) {}
         }
     }