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[BUG] Java Feign Client produces ClassCastException for methods returning Object

Created by: lbilger

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

When I have an operation that returns Object, the ApiResponseDecoder will throw a ClassCastException because it tries to cast a Class to ParameterizedType.

openapi-generator version

5.4.0

OpenAPI declaration file content or url

see the reproducer linked below.

Generation Details
                            <generatorName>java</generatorName>
                            <library>feign</library>
                                <feignVersion>11.x</feignVersion>
Steps to reproduce

I have created a minimal reproducer in this GitHub repository. The maven build mvn clean test will report a test failure with feign.codec.DecodeException: class java.lang.Class cannot be cast to class java.lang.reflect.ParameterizedType.

Related issues/PRs

I will create a PR soon.

Suggest a fix

I will create a PR soon.