A schema in components/schemas with type: ["object", "null"] that has a nested model, for example a property that is itself a nullable object, is dropped with Attempted to generate duplicate models with name "...Type0". Every schema that references it is dropped too. The generator exits 0 and only prints "Client was generated, but some pieces may be missing".

Minimal spec:

components:
  schemas:
    Outer:
      type: object
      properties:
        inner:
          $ref: "#/components/schemas/Inner"
    Inner:
      type: ["object", "null"]
      properties:
        labels:
          type: ["object", "null"]
          additionalProperties: { type: "string" }

Cause: _create_schemas calls property_from_data with process_properties=False, so that model properties are built later in _process_models. UnionProperty.build splits a type list into one variant per type and calls property_from_data for each, but it did not forward process_properties or roots. The object variant was therefore built immediately, which registered InnerLabelsType0. The same variant is also in models_to_process, so building it again in _process_models registered the same name a second time and failed.

This forwards process_properties and roots from property_from_data through UnionProperty.build to its variants. anyOf/oneOf unions go through the same code path and get the same fix.

Changes:

• union.py: UnionProperty.build takes process_properties and roots and passes them to the variants.
• properties/__init__.py: property_from_data passes both to UnionProperty.build.
• New functional test TestNullableTopLevelObjectWithNullableProperty in test_unions.py.
• Patch changeset.

Testing:

• The new test errors on main and passes with this change.
• pytest tests end_to_end_tests: 468 passed, 4 skipped. The golden records are unchanged.
• ruff check, ruff format --check and mypy pass.