[BUG] openapi-generator is generating different code without and with default mustache templates

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

The openapi-generator command line tool is generating Python FastAPI server code (python-fastapi) from the pet store API specs. In the first run without explicit templates. In the second run with the default templates in the openapi-generator repository.

openapi-generator generate -g python-fastapi -i petstore.yaml -o .
openapi-generator generate -g python-fastapi -i petstore.yaml -o . -t default_templates

Expected behaviour: The generated code is identical in both cases.
Actual behaviour: The generated code differs.

openapi-generator version

6.6.0 on macOS 13.4.1

OpenAPI declaration file content or url

An example is given in this public repository. The current openapi-generator repository is added as submodule. For the example we make use of the pet store specs and the python-fastapi mustache templates.

This commit shows the difference of the generated code with and without explicit -t templates.

Generation Details

See this public repository and above.

Steps to reproduce

Run the generate.sh script without and with templates.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/16200

Suggest a fix

None.

Start with the generate.sh script and reproduce both commands using petstore.yaml, comparing output with and without the default_templates directory. Inspect the python-fastapi templates under modules/openapi-generator/src/main/resources/python-fastapi and the related issue #16200; done means both generation paths produce identical code.