[BUG] Error generating TypeScript when request body includes discriminated union

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)? (used Redocly struct linter)
• 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

Spec with a discriminated union in a request produces error:

[main] ERROR o.o.codegen.DefaultCodegen - Error in generating example for the property SchemaForRequestBodyApplicationJson. Default to ERROR_TO_EXAMPLE_VALUE. Enable debugging for more info.

openapi-generator version

7.12.0

OpenAPI declaration file content or url

Link to minimum reproducible spec

Generation Details

I've put up a full reproduction at https://github.com/collinsauve/testing-openapi-generator-cli that includes the above linked spec and a few others that demonstrate a bit more of the problem space.

Without using that, the command is:

npx @openapitools/openapi-generator-cli generate -g typescript -i "spec.yaml" -o "output"

Steps to reproduce

1. Clone https://github.com/collinsauve/testing-openapi-generator-cli
2. Run bin/test test3-union-with-two-types

Related issues/PRs

• Same error as https://github.com/OpenAPITools/openapi-generator/issues/8663
• Originally reported via https://github.com/planet-a-ventures/affinity-node/pull/70 by @joscha in when using this generator on one of our (Affinity.co's) specs.

Suggest a fix

Start by running the bin/test test3-union-with-two-types reproduction from the linked repository, or invoke the TypeScript generator with the linked test3-union-with-two-types.yaml spec. Trace the DefaultCodegen example-generation error and compare the generated output with the expected handling of the discriminated union; done means generation completes without the reported error.