Keep full backward compat with disabling cell mapping

this is a follow up to I8aa77e5ebd1618dadd7e0a72d51e9b6a11b44f43

To keep the default behaviour intact for any model, we should
default to as if update_cells is present and is True.
Otherwise when the updated_cells key is missing, the current construct
is evaluated to None, and cell mapping is skipped.

Related-Issue: PROD-34645
Change-Id: I93fb74fe39c642a4749c05c6cb5d9a5df9c62bf7
2 files changed