Fix #228 -- Skip migration for objects without files

[jmsmkn]

Close #228

[jmsmkn]

There are existing tests already to ensure that the migrations are carried out for objects with pictures and that nothing is done for objects without pictures, this PR is just making that 2nd step more direct.

[codingjoe]

Nice! But just to be safe, be so kind and add a test case to prevent regression in future versions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (32289a5) to head (8528f53).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #230   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines          495       495           
=========================================
  Hits           495       495           

Flag	Coverage Δ
celery	85.05% <0.00%> (ø)
cleanup	88.48% <100.00%> (ø)
dj4.2	88.48% <100.00%> (ø)
dj5.1	88.48% <100.00%> (ø)
django-rq	85.05% <0.00%> (ø)
dramatiq	85.05% <0.00%> (ø)
drf	96.36% <100.00%> (ø)
macos-latest	88.68% <100.00%> (ø)
py3.10	88.48% <100.00%> (ø)
py3.11	88.48% <100.00%> (ø)
py3.12	88.48% <100.00%> (ø)
py3.13	88.48% <100.00%> (ø)
py3.14	88.48% <100.00%> (ø)
ubuntu-latest	88.48% <100.00%> (ø)
windows-latest	81.58% <100.00%> (ø)

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[codingjoe]

I took the liberty of adding them :)

[Copilot]

Pull request overview

This PR fixes issue #228 by adding logic to skip database objects that have empty or null file fields during migrations. This prevents errors when the migration code attempts to process file operations on non-existent files.

• Added filtering to exclude objects with empty ("") or None values in the picture field before processing
• Applied the fix consistently across all three migration methods
• Added comprehensive test coverage for each migration method to verify the fix

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pictures/migrations.py	Added .exclude(Q(**{self.name: ""}) | Q(**{self.name: None})) filtering to update_pictures, from_picture_field, and to_picture_field methods to skip objects without files
tests/test_migrations.py	Added three new test methods (test_update_pictures__with_empty_pictures, test_from_picture_field__with_empty_pictures, test_to_picture_field__with_empty_pictures) to verify that migrations correctly handle mixed scenarios with both populated and empty picture fields

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