Fix test

src/main/java/net/minestom/server/entity/Player.java

@@ -1081,6 +1081,7 @@ public class Player extends LivingEntity implements CommandSender {
     @Override
     protected void onAttributeChanged(@NotNull final AttributeInstance attributeInstance) {
         if (attributeInstance.getAttribute().isShared() &&
+                playerConnection != null &&
                 playerConnection.getConnectionState() == ConnectionState.PLAY) {
             playerConnection.sendPacket(getPropertiesPacket());
         }