Fix #462 -- Allow _bulk_create=True without _quantity

[amureki]

Describe the change
Allows baker.make(Model, _bulk_create=True) to work without specifying _quantity. In this case it returns a single object (not a list), which is consistent with the usual make() behavior.

PR Checklist

• Change is covered with tests
• CHANGELOG.md is updated if needed

Summary by CodeRabbit

• New Features
  • The _bulk_create parameter can now be used independently without requiring _quantity specification, returning a single created instance when _quantity is not provided.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request modifies the baker.make method to support _bulk_create=True without requiring an explicit _quantity parameter. When _quantity is None, bulk_create is invoked with a default quantity of 1 and returns a single instance. When _quantity is provided, the method returns a list. A corresponding test case and changelog entry document this behavioral change.

Changes

Cohort / File(s)	Summary
Core Implementation model_bakery/baker.py	Modified Baker.make to always call bulk_create when _bulk_create is True, regardless of _quantity. Returns a single instance (result[0]) when _quantity is None, or the full list when _quantity is provided.
Test Coverage tests/test_baker.py	Added test_make_bulk_create_without_quantity to verify bulk_create is invoked when _bulk_create=True and _quantity is None, confirming a valid Person instance is returned.
Documentation CHANGELOG.md	Documented that _bulk_create can now be used with True without requiring _quantity.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Fix _bulk_create for ManyToManyField with custom through models (#477) #570: Addresses bulk_create ManyToMany through-model foreign key name handling — related through bulk_create integration changes.

Poem

🐰 A baker's twist, so clean and bright,
No \_quantity needed, the logic feels right!
One bulk create call, a list or alone,
The baker now serves with more finesse shown. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly relates to the main change: allowing _bulk_create=True without _quantity. It references the fixed issue #462 and clearly summarizes the primary enhancement.

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✨ Finishing touches

• 📝 Generate docstrings

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