Notifies this listener that the associated session's client has disconnected. If {@code graceful} is {@code true}, then the session's client logged out gracefully; otherwise, the session was either disconnected forcibly by the server or disconnected due to other factors such as communication failure.
If this listener does not implement {@link ManagedObject}, it will be removed from the persistent store after this method returns. Otherwise, this listener will remain in the persistent store until it is explicitly {@linkplain DataManager#removeObject removed}.
When this method is invoked, the client session associated with this listener will have already been removed if the application removed the client session in order to disconnect it. If the client session has not yet been removed and this method does not remove the client session, the client session will be removed in the same transaction after this method returns.
@param graceful if {@code true}, the specified client session logged out gracefully