Missing references in API generation process

Start with the create-a-new-client instructions linked in the issue and reproduce the warning using the reported OpenAPI client generation process. Investigate why the Index, IndexInSpec, and IndexParams references are removed, then confirm that generation completes without the warning and preserves those schemas.

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