Javadoc
When overridden . This method is called whenever a connector needs some
extra computation to save its old value. By default, the method returns the
parameter itself. For instance, this method is overridden in collection
connectors, where the underlying collection does not change but its content
changes. Simply keeping a reference on the underlying collection would not
be of any help since it never changes, preventing the notification to
happen. In that case, a clone of the model collection can be built to keep
track of the collection content change.