[BUG] [Rust] Rust-reqwest client fails because of null values in tags arrays from petstore.swagger.io

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

The rust-reqwest client fails on the current contents of petstore.swagger.io because of null values in the tags array of some pets.

openapi-generator version

4.1.2-SNAPSHOT

OpenAPI declaration file content or url

See http://petstore.swagger.io/v2/swagger.json

Command line used for generation

docker run --rm -v ${PWD}:/local/out/rust/ openapitools/openapi-generator-cli generate \
    -i http://petstore.swagger.io/v2/swagger.json \
    -g rust -o /local/out/rust/generated \
    --additional-properties packageName=petstore_client \
    --library=reqwest

Steps to reproduce

1. Generate the client as above.
2. Use it to call find_pets_by_status.
3. See the following error.

result = Err(Reqwest(Error(Json(Error("invalid type: null, expected struct Tag", line: 1, column: 2807)))))

Also, this is currently in the petstore api:

$ curl -X GET "https://petstore.swagger.io/v2/pet/findByStatus?status=pending" -H  "accept: application/json" | jq ".[].tags"
...
[
  null
]
...

And this is the relevant spec section:

$ curl --silent --output - http://petstore.swagger.io/v2/swagger.json | jq ".definitions.Pet.properties.tags"
{
  "type": "array",
  "xml": {
    "name": "tag",
    "wrapped": true
  },
  "items": {
    "$ref": "#/definitions/Tag"
  }
}

Related issues/PRs

No related issues found.

Suggest a fix

To get it working, I had to change this line in the Pet model:

    pub tags: Option<Vec<crate::models::Tag>>,

To this:

    pub tags: Option<Vec<Option<crate::models::Tag>>>,

Although I don't know whether those nulls should have even been allowed in the first place.

Start by running the provided Docker generation command against the petstore.swagger.io spec, then call find_pets_by_status with the generated rust-reqwest client. Compare the generated Pet model's tags field with the response containing null entries. Done means the generated client handles that response without the null-deserialization error and remains consistent with the tags schema.