This has important side effect that matters when we check for data
changes using _orig dictionary. Previously, _orig was empty (so its
members fields were undefiend) whereas the real fields were declared as
nulls. This meant that for new entities, the conditions were always
true, which is unintended. Now both _orig and the class itself are
initially populated with _updateFromResponse which syncs the state
between them, removing the problem.
