[BUG] dart-dio Unsupported operation: more than one match found

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

In runtime, dart-dio fails to deserialize oneOf.

openapi-generator version

6.5.0

OpenAPI declaration file content or url

https://raw.githubusercontent.com/TeamPiped/OpenAPI/main/swagger.yaml

Generation Details

npx @openapitools/openapi-generator-cli generate -i swagger.yaml -c dart.yaml -g dart-dio -o ../code/

dart.yaml:

pubLibrary: piped
pubName: piped_api
pubDescription: Automatically generated OpenAPI bindings for Piped.

Steps to reproduce

Generate the code, run a test with the default URL.

Related issues/PRs

N/A, oneOf support was added a while back tho

Suggest a fix

Not sure unfortunately why this happens :(

Start by running the listed openapi-generator command with the linked swagger.yaml and inspect the generated dart-dio runtime where oneOf deserialization handles multiple matches. Reproduce the failure using the default URL, then verify that the generated client deserializes the response without the “more than one match found” error.