Immutable entities can now be saved and loaded and the immutability will be honored.
This feature is currently limited to a single level of reference.
In order to implement this the logic for updating IDs with those generated from the database got moved out of the DefaultDataAccessStrategy into the AggregateChange.
As part of that move DataAccessStrategy.save now returns a generated id, if available.
See also: DATAJDBC-248.
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