All request headers marked as required for Java controllers in mixed projects in 2.0.3

[petergphillips]

Similar to #2170 but for request headers instead of request parameters. Tested with 2.0.5-SNAPSHOT and bug still remains.

Describe the bug
We've got some large projects that we are gradually converting to Kotlin. For those projects we have a mix of Java and Kotlin rest controllers.
Under 2.0.2 in the Java controllers the required parameter of @RequestHeader was honoured. Under 2.0.3 / 2.0.4 it appears that this parameter is completely ignored. Furthermore adding in a @Parameter(required = false) annotation has no effect either.
So

    @GetMapping("/")
    public Greeting greet(@RequestHeader(required = false) @Parameter(required = false) final String name) {
        return new Greeting(name);
    }

always generates a required parameter:

To Reproduce

• What version of spring-boot you are using? 3.0.4
• What modules and versions of springdoc-openapi are you using? springdoc-openapi-starter-webmvc-ui 2.0.4
• What is the actual and the expected result using OpenAPI Description (yml or json)?
  Actual is

                "parameters": [
                    {
                        "in": "header",
                        "name": "name",
                        "required": true,
                        "schema": {
                            "type": "string"
                        }
                    }
                ],

Expected is

                "parameters": [
                    {
                        "in": "header",
                        "name": "name",
                        "required": false,
                        "schema": {
                            "type": "string"
                        }
                    }
                ],

• Provide with a sample code (HelloController) or Test that reproduces the problem
  Sample controller is

@RestController
public class OptionalHeaderController {
    @GetMapping("/")
    public Greeting greet(@RequestHeader(required = false) final String name) {
        return new Greeting(name);
    }
}

Sample project demonstrating the issue (including test case) can be found at https://github.com/petergphillips/springdoc-optional-parameters.

Expected behavior
We weren't expecting the upgrade of spring boot / spring docs to change the OpenAPI documentation for of all our Java controllers. The fix appears to be either to convert all our controllers to Kotlin or setting

springdoc.nullable-request-parameter-enabled = false

The latter change then means that we can't take advantage of the improvement in #2006 in our Kotlin controllers.
It also seems odd that the upgrade should change the behaviour in this way, perhaps the code should take into account whether it is a Java controller and if so then not to look at the nullability of the parameter to determine if it is required.

[bnasslahsen]

@petergphillips,

I have added a better fix. Let me know if this one is better!

[petergphillips]

Just had a check of our project and looking good 👍 , thanks