[BUG] Compilation error on models when supporting files (JSON.java,RFC3339DateFormat.java) are not generated

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

When generating just model objects using the java generator compilation fails if supporting files are not generated because of unused import org.openapitools.client.JSON.

openapi-generator version

6.0.1 (also occurs in 7.0.0-SNAPSHOT)

OpenAPI declaration file content or url

https://github.com/peter-janssen/openapi-bug/blob/3733981bca3bb82373707aad9a850f3141babc9d/src/main/resources/openapi.yaml

Generation Details

https://github.com/peter-janssen/openapi-bug/blob/3733981bca3bb82373707aad9a850f3141babc9d/pom.xml#L111

Steps to reproduce

Generate models with supporting files set to false.
See https://github.com/peter-janssen/openapi-bug (run .mvnw compile results in a compilation error)

Related issues/PRs

Somewhat related:
https://github.com/OpenAPITools/openapi-generator/issues/7177

Suggest a fix

It is unclear to me what exactly the purpose of org.openapitools.client.JSON but a naive suggestion would be not to add the import when it is not used or make it toggleable .

Workaround

To prevent all supported files to be generated it can be limited using:

<supportingFilesToGenerate>JSON.java,RFC3339DateFormat.java</supportingFilesToGenerate>

Start with the linked openapi.yaml and pom.xml generation configuration, then reproduce the failure by running .mvnw compile with supporting files disabled. Inspect the generated model imports and the generator's handling of JSON.java and RFC3339DateFormat.java. Done means model-only generation compiles without requiring omitted supporting files.