Merge remote-tracking branch 'origin/master'

Author: GuilhermeJ

lib/src/main/java/ua/naiksoftware/stomp/OkHttpConnectionProvider.java

@@ -37,7 +37,9 @@ class OkHttpConnectionProvider extends AbstractConnectionProvider {
     @NonNull
     @Override
     public void rawDisconnect() {
-        openedSocked.close(1000, "");
+        if (openedSocked != null) {
+            openedSocked.close(1000, "");
+        }
     }
 
     @Override

lib/src/main/java/ua/naiksoftware/stomp/client/StompClient.java

@@ -186,8 +186,12 @@ public void disconnect() {
     }
 
     public Completable disconnectCompletable() {
-        mLifecycleDisposable.dispose();
-        mMessagesDisposable.dispose();
+        if (mLifecycleDisposable != null) {
+            mLifecycleDisposable.dispose();
+        }
+        if (mMessagesDisposable != null) {
+            mMessagesDisposable.dispose();
+        }
         return mConnectionProvider.disconnect()
                 .doOnComplete(() -> setConnected(false));
     }