Time triggered batch update does not accept null value

[wgromniak]

userStream.updateTimeTriggeredBatch(id, 1000, null, null);

causes

net.quedex.api.common.CommunicationException: Error sending message
	at net.quedex.api.user.UserMessageSender.lambda$sendMessageQueued$7(UserMessageSender.java:168)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: null
	at net.quedex.api.user.UserMessageSender.createBatchNode(UserMessageSender.java:151)
	at net.quedex.api.user.UserMessageSender.lambda$sendTimeTriggeredBatchUpdate$4(UserMessageSender.java:123)
	at net.quedex.api.user.UserMessageSender.lambda$sendMessageQueued$7(UserMessageSender.java:164)
	... 3 common frames omitted

@mchalapuk, @HubertBubert, CC.