StackOverflowError when using Kotlin companion object's fields

[komarovd95]

Describe the bug
Hi there. I faced a problem with generating OpenAPI specification using Kotlin.

I have a parameter in the RestController's method annotated with ParameterObject. The type of this parameter is a Kotlin class with companion object which have a non-const members (fields and/or properties). In my case it has read-only property of type java.time.Duration. When I'm accessing an OpenAPI specification via /v3/api-docs endpoint I'm getting a StackOverflowError at line MethodParameterPojoExtractor:113.

Annotating this property with a JvmField annotation nor JvmStatic didn't help.

I did some debug and realized that the MethodParameterPojoExtractor#extractFrom method is falling into recursion with the Duration.ZERO field which is static too.

To Reproduce
I'm using:
Spring 5.2.4.RELEASE
Spring Boot 2.2.5.RELEASE
SpringDoc OpenAPI 1.5.6
Kotlin 1.4.31

There is an example controller with which it can be reproduced:

@Tag(name = "Some API")
@RestController
@RequestMapping("/example")
class ExampleController {

    @GetMapping(produces = [MediaType.TEXT_PLAIN])
    @Operation(summary = "My awesome operation")
    fun test(@ParameterObject request: TestRequest): ResponseEntity<String> {
        return ResponseEntity.ok("test")
    }
}

class TestRequest(
    @field:Parameter(description = "Some parameter")
    val param: String
) {

    companion object {
        val SOME_CONSTANT_DURATION = Duration.ofHours(1L)
    }
}

So if you try to access http://localhost:8080/v3/api-docs you will receive HTTP status code 500 and StackOverflowError stack trace in the logs.

Expected behavior
So I think it should be allowed to use such classes as a parameter annotated with ParameterObject.

Maybe it's not needed to collect static fields in the MethodParameterPojoExtractor#allFieldsOf method.

[bnasslahsen]

@komarovd95,

This is related to Duration which is not resolved as a Swagger Primitive Type.
Make sure you declare it for the @ParameterObject.

static {
	SpringDocUtils.getConfig().addSimpleTypesForParameterObject(Duration.class);
}

It will be handled out of the box for the next release.