[BUG] openapi-generator problem with nested oneOf?

Description

The openapi-generator client generation crashes on the provided OpenAPI document, which passes validation both using openapi-generator validate and linting using speccy. It seems to be language independent (affects all languages I tried).

openapi-generator version

4.0.0-beta3

OpenAPI declaration file content or url

Gist of JSON here:
https://gist.github.com/einarwh/c8526951c3080ddca7b3b791066bb9e3

Command line used for generation

No fancy options, just:
openapi-generator generate -i openapi.json -g csharp

Steps to reproduce

Save gist as e.g. openapi.json and run:
openapi-generator validate -i openapi.json
to verify that the document is valid and then
openapi-generator generate -i openapi.json -g csharp
to get error message complaining about 'ResourceId' model.

Related issues/PRs

Looks very similar to this:
https://github.com/OpenAPITools/openapi-generator/issues/2610

Suggest a fix/enhancement

It seems that the problem is due to nested oneOf's.

Use the linked gist as openapi.json; first run validate, then run generate -g csharp and capture the ResourceId failure. Trace how the generator handles the nested oneOf models, and consider the issue complete when this valid document generates successfully without the reported crash.