Client ID can be null

I think there is an issue handling null client IDs. From what I know (and I may be wrong here) client IDs may be null when requesting a subscription.

And currently this works fine in Milo with the exception of handling the server result after the subscriptions succeeded:

OpcUaSubscription.java:130

if (item.getStatusCode().isGood()) {
  itemsByClientHandle.put(item.getClientHandle(), item);
  itemsByServerHandle.put(item.getMonitoredItemId(), item);
}

I think this could be fixed with ignoring null client IDs altogether in this case.

[kevinherron]

In the next version of my code generator I’ll try to put @Nonnull annotations on any of the parameters I can determine shouldn’t ever be null.

[ctron]

There is no scenario where creating a monitored item and providing a null clientHandle in the MonitoredItemCreateRequest is the correct behavior.

After digging a bit into the issue and into the OPC UA code at https://github.com/OPCFoundation/UA-.NET/blob/master/Stack/Core/Stack/Generated/Opc.Ua.Client.cs#L2807 I think you are right, the clientHandle should never be null.

But that isn’t obvious from the API of Milo. So I would suggest to either directly check for null in the constructor or at least add some JavaDoc for that.