[ahinoamp]

Problem

RevisionsMixin.push_delta dereferences find_instance(msg["id"]) unconditionally:

key = self._track_revisions(self.find_instance(msg["id"]))

The instance registry holds weak references, so a delta flushed after its model was collected resolves to None. The whole flush then dies with AttributeError: 'NoneType' object has no attribute '_id'.

Change

When the instance is gone, the delta is published without a revision. get_state already answers {"id": ..., "state": None} for such an id, so what to do about a dropped instance stays with the client.

Test

test_a_delta_for_a_collected_model_is_published_without_a_revision runs on both protocol versions. It fails on the current code (2 failed) and passes with the change (22 passed in tests/test_protocol_revisions.py).

🤖 Generated with Claude Code

[alesgenova]

can you share more information about what issue prompted you to implement this fix?
the only pathway I can find is that if we create a deepcopy of a model instance it gets the same id as the original.
If the original instance gets later collected, we end with a possible crash.
Also having one id pointing to two instances is clearly a problem on its own.
Anyway, can you confirm whether the issue stemmed from copying a model instance? If so, the real fix would be to implement proper copying