[BUG][Java/spring] useOptional:true is applied only if openApiNullable:true

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)

OpenAPI declaration file content or url

openapi: 3.0.0
components:
  schemas:
    Item:
      type: object
      properties:
        foo:
          type: string

Description

Assume we have a very minimal specification (see above) and use Java Spring Boot generator.

With useOptional:true everything is fine i.e.

public class Item {
  private Optional<String> foo = Optional.empty();

  public Item foo(String foo) {
    this.foo = Optional.ofNullable(foo);
    return this;
  }

  @JsonProperty("foo")
  public Optional<String> getFoo() {
    return foo;
  }

  public void setFoo(Optional<String> foo) {
    this.foo = foo;
  }
}

... but Optional wrappers are applied only if openApiNullable:true.
Luckily, it is a default behavior. Still, if I explicitly turn it off openApiNullable:false then useOptional:true doesn't have any effect

public class Item {
  private String foo;

  public Item foo(String foo) {
    this.foo = foo;
    return this;
  }

  @JsonProperty("foo")
  public String getFoo() {
    return foo;
  }

  public void setFoo(String foo) {
    this.foo = foo;
  }
}

I guess it is a bug. The output should be the very same as above.

Or am I missing an idea behind it? Is it written somewhere in documentation that useOptional makes sense only together with openApiNullable?

@MelleD as you seem to be an expert of using Optional, what are your thoughts of it?
Should I provide a PR to fix?

openapi-generator version

7.10.0

Start with the Java Spring Boot generator and reproduce the issue using the minimal OpenAPI schema in the report. Compare generated Item models with useOptional:true while toggling openApiNullable. Done means Optional wrappers are generated when useOptional is enabled, regardless of the openApiNullable setting, with coverage for both option combinations.