[BUG] Gradle plugin produces uncompilable code for GitHub definition file.

Bug Report Checklist

• [yes] Have you provided a full/minimal spec to reproduce the issue?
• [ think so ] Have you validated the input using an OpenAPI validator (example)?

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I tried this validator with this cut-down schema and it looked like it was happy, but I'm not an expert.

• [yes ] Have you tested with the latest master to confirm the issue still exists?
• [ yes ] Have you searched for related issues/PRs?
• [ yes ] What's the actual output vs expected output?

Expected: There should be some fields in all kotlin data classes.
Actual: None

Description

Generating the GitHub API schema for Kotlin results in a data class without fields, which doesn't compile. I've extracted and pared down a single endpoint in the gist.

In data.class.mustache, allVars is empty, even though hasVars is true and nonNullableVars, optionalVars, and readWriteVars all contain (in the example Gist) reviewers and teamReviewers.

openapi-generator version

My target version is 7.12.0 but it happens with :latest too, see above.

OpenAPI declaration file content or url

https://gist.githubusercontent.com/sleekweasel/bd91330c7c437d1641a52761d18d8d60/raw/a9fcef66c20938b762944f3d938cbcee1f483fc5/api.chopped.json

Generation Details

$ curl -o https://gist.githubusercontent.com/sleekweasel/bd91330c7c437d1641a52761d18d8d60/raw/a9fcef66c20938b762944f3d938cbcee1f483fc5/api.chopped.json

$ docker run -v $PWD:$PWD  openapitools/openapi-generator-cli:v7.12.0  generate -i api.chopped.json -g kotlin  -o $PWD

$ grep -A2 data src/main/kotlin/org/openapitools/client/models/PullsRequestReviewersRequest.kt
data class PullsRequestReviewersRequest (

) {

Steps to reproduce

See above. There are no entries in data class, which means it won't compile.

Related issues/PRs

Suggest a fix

Start with the cut-down schema in the linked gist and reproduce the Kotlin output using the provided Docker generation command. Inspect data.class.mustache, especially the allVars, hasVars, nonNullableVars, optionalVars, and readWriteVars values. Done means PullsRequestReviewersRequest.kt contains the expected reviewers and teamReviewers fields and compiles.