Null pointer Exception on every action smack 4.4.2

[Saba_Zafar]

I create group using multiUserChat.create(nickname) and join multiUserChat.join(Resourcepart.from(userName));
soon after this everything works fine. but when I kill app and again open the app, following error appear on message sending, send typing status.

sending message using
multiUserChat.sendMessage(smackMessage.asBuilder());