FieldTracker.finalize_class raises AttributeError when used with django-positions PositionField

[iarp]

Problem

Using django-positions PositionField on the model. Adding tracker = FieldTracker() causes the following exception to run at runtime preventing the server from starting

  File "F:\Projects\myproj\venv\lib\site-packages\model_utils\tracker.py", line 338, in finalize_class
    descriptor = getattr(sender, field_name)
  File "F:\Projects\myproj\venv\lib\site-packages\positions\fields.py", line 144, in __get__
    raise AttributeError("%s must be accessed via instance." % self.name)
AttributeError: display_order must be accessed via instance.

PositionField.__get__ raises AttributeError if you attempt to getattr on its field as seen here https://github.com/jpwatts/django-positions/blob/master/positions/fields.py#L142

I was able to fix this by changing FieldTrackers use of descriptor = getattr(sender, field_name) to descriptor = getattr(sender, field_name, None)

I'm unsure which package should be the one to update though.

Environment

• Django Model Utils version: 4.3.1
• Django version: 4.2.4
• Python version: 3.10.7
• Other libraries used, if any:
• django-positions 0.6.0

Code examples

class PlaylistItem(models.Model):

    field_tracker = FieldTracker()

    display_order = PositionField(default=-1)