You are seeing this exception because this line is the one executed when you void an obs and even though the method return an instance of the saved obs, it has not been assigned to this variable which is not supposed to be null when this line is executed. A quick fix would be to do the assignment. But the question here is, is it really desirable to display the voided obs? because that is what is going to happen if this code is fixed that way. IMO I think we don’t and probably this should be handled differently, I am open to hear others ideas.
In the mean time you can go ahead and create a ticket on the legacy UI project with exactly the same details.