Fix REntityServer NPE

SpigotCore_Main/src/de/steamwar/entity/REntityServer.java

@@ -146,9 +146,12 @@ public class REntityServer implements Listener {
     }
 
     private void onMissing(HashSet<Player> of, HashSet<Player> in, Consumer<Consumer<Object>> packetProvider) {
+        if(of == null)
+            return;
+
         for(Player player : of) {
-            if(!in.contains(player)) {
+            if(in == null || !in.contains(player)) {
-                packetProvider.accept(packet -> TinyProtocol.instance.sendPacket(player, packet)); //TODO multi packet generation
+                packetProvider.accept(packet -> TinyProtocol.instance.sendPacket(player, packet));
             }
         }
     }