NPE disposing of a Disposable

[steviemo]

We got this exception in from firebase from our Android application:

Exception java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.Set.iterator()' on a null object reference
ua.naiksoftware.stomp.client.StompClient.lambda$topic$3 (StompClient.java:183)
ua.naiksoftware.stomp.client.StompClient$$Lambda$5.run ()
io.reactivex.internal.operators.flowable.FlowableDoOnLifecycle$SubscriptionLambdaSubscriber.cancel (FlowableDoOnLifecycle.java:112)
io.reactivex.internal.subscriptions.SubscriptionHelper.cancel (SubscriptionHelper.java:189)
io.reactivex.internal.operators.flowable.FlowableSubscribeOn$SubscribeOnSubscriber.cancel (FlowableSubscribeOn.java:141)
io.reactivex.internal.operators.flowable.FlowableObserveOn$BaseObserveOnSubscriber.cancel (FlowableObserveOn.java:154)
io.reactivex.internal.subscriptions.SubscriptionHelper.cancel (SubscriptionHelper.java:189)
io.reactivex.internal.subscribers.LambdaSubscriber.cancel (LambdaSubscriber.java:116)
io.reactivex.internal.subscribers.LambdaSubscriber.dispose (LambdaSubscriber.java:101)

I'll raise a PR with the null check now.

[steviemo]

#83

[NaikSoftware]

Check new version 1.4.4