[Rust] fix for required nullable input generating invalid code (!12485) · Merge requests · OpenAPI Tools / openapi-generator

Created by: gaetronik

When a parameter is both required and nullable the code generate an Option<&str> parameters and then try to do a to_string() on this paramter which failed due to lack of to_string() implementation for Option<&str>. An example of such issue can be found in https://developers.scaleway.com/static/c78c1fb6947abf78efab65d4acc6dacd/scaleway.baremetal.v1.Api.yml in function list-settings

@frol @farcaller @richardwhiuk @paladinzh

Read the contribution guidelines.
Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
Run the following to build the project and update samples:
```
./mvnw clean package 
./bin/generate-samples.sh
./bin/utils/export_docs_generators.sh
```
Commit all changed files. 2484 This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
File the PR against the correct branch: master (6.0.1) (patch release), 6.1.x (breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.