[BUG] [Spring] Nullable annotation not imported in Spring-Boot controllers

[jpfinne]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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?
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Description

Compilation error for generated spring-boot generated rest controller.
@Nullable annotation is set for NativeWebRequest. The annotation is not imported in all cases. For example when the operations have only required arguments.

openapi-generator version

7.22.0-SNAPSHOT

OpenAPI declaration file content or url

Generation Details

java -jar openapi-generator-cli.jar generate -g spring --library spring-boot -i modules/openapi-generator/src/test/resources/3_0/petstore.yaml -o /tmp/output

Steps to reproduce

The generated /tmp/output/src/main/java/org/openapitools/api/UserApiController.java
contains a @Nullable annotation, but no import.

It gives a compilation error

Related issues/PRs

Regression due to #23256

Suggest a fix

Quick fix: remove the annotation from apiController.mustache
Mid term fix:

correclty add @Nullable annotation in all the java and spring generators. The goal is is to avoid false alarms when using JSpecify. Ensure that @Nullable annotations are correctly imported