val selectedSessionOrThrow: Session (source)
Gets the currently selected session or throws an IllegalStateException if no session is selected.
It's application specific whether a session manager can have no selected session (= no sessions) or not. In applications that always have at least one session dealing with the nullable selectedSession property can be cumbersome. In those situations, where you always expect a session to exist, you can use selectedSessionOrThrow to avoid dealing with null values.
Only one session can be selected at a given time.