Missing references in API generation process

issue にリンクされている create-a-new-client の手順から始め、報告されている OpenAPI クライアント生成プロセスを使って警告を再現します。Index、IndexInSpec、IndexParams の参照が削除される理由を調査し、その後、警告なしで生成が完了し、これらのスキーマが保持されることを確認します。

Describe the bug
While trying to generate the OpenAPI client, I come across a bug that not only modifies several files unnecessarily but also displays a warning message about endpoint generating, which root cause is unclear to me:

Warning(s) encountered while generating. Client was generated, but some pieces may be missing

WARNING parsing POST /index/create within index. Endpoint will not be generated.

Could not find reference in parsed models or enums



Unable to process schema /components/schemas/Index:

Value {'object_type': 'IndexParams', 'nlist': 128} is not valid, only None is allowed

Failure to process schema has resulted in the removal of:
/components/schemas/Index
/components/schemas/IndexInSpec

Schema(title=None, multipleOf=None, maximum=None, exclusiveMaximum=None, minimum=None, exclusiveMinimum=None, maxLength=None, minLength=None, pattern=None, maxItems=None, minItems=None, uniqueItems=None, maxProperties=None, minProperties=None, required=None, enum=None, const=None, type=None, allOf=[], oneOf=[Reference(ref='#/components/schemas/IndexParams'), Schema(title=None, multipleOf=None, maximum=None, exclusiveMaximum=None, minimum=None, exclusiveMinimum=None, maxLength=None, minLength=None, pattern=None, maxItems=None, minItems=None, uniqueItems=None, maxProperties=None, minProperties=None, required=None, enum=None, const=None, type=<DataType.NULL: 'null'>, allOf=[], oneOf=[], anyOf=[], schema_not=None, items=None, properties=None, additionalProperties=None, description=None, schema_format=None, default=None, nullable=False, discriminator=None, readOnly=None, writeOnly=None, xml=None, externalDocs=None, example=None, deprecated=None)], anyOf=[], schema_not=None, items=None, properties=None, additionalProperties=None, description=None, schema_format=None, default={'object_type': 'IndexParams', 'nlist': 128}, nullable=False, discriminator=Discriminator(propertyName='object_type', mapping=None), readOnly=None, writeOnly=None, xml=None, externalDocs=None, example=None, deprecated=None)

OpenAPI Spec File
A link to an OpenAPI document which produces this issue. Ideally, write a minimal reproduction only containing the problematic pieces.
Creating the new client: https://github.com/openapi-generators/openapi-python-client?tab=readme-ov-file#create-a-new-client

Desktop (please complete the following information):

• OS: Windows 11 Enterprise Version 22H2
• Python Version: 3.9.13
• openapi-python-client version: 0.17.2