Called as the first operation of the handOverTo() function. 

This function allows custom classes to populate the new object. Overriding this function in a child class allows a child instance to be notified each time an object is handed over. This function is notified just before an object is to be handed over, giving this function the ability to cancel the handover. When overriding this function: 1) If the OdDgElements's state is incorrect, throw an exception. 2) Call the parent class's subHandover(). 3) If other actions are required before handover, do them. The default implementation of this function does nothing. This function can be overridden in custom classes.