[BUG] [Go] XML array is always present even if nullable and not required (missing pointer on slice)

Description

When I generate an array with nullable set to true, we don't have a pointer on the generated slice even if the field is not required.
During marshalling of the generated struct, if the slice is empty:

• with JSON, the omitempty option allows to have the deletion of the field containing the slice
• with XML, if the slice is empty, the field always is present.

With the below swagger.yaml, we obtain:
actual struct:

type Command struct {
	// List of Items
	Structmember []Item `json:"struct>member,omitempty" xml:"struct>member"`
}

expected struc:

type Command struct {
	// List of Items (with a pointer)
	Structmember *[]Item `json:"struct>member,omitempty" xml:"struct>member"`
}

And with this test, we see that, without pointer, we obtain a different behavior between JSON and XML:

package model

import (
	"encoding/json"
	"encoding/xml"
	"fmt"
	"testing"
)

func TestNewCommand(t *testing.T) {
	cmd := Command{}

	buff, _ := json.Marshal(cmd)
	fmt.Println("- With JSON: ", string(buff))
	buff, _ = xml.Marshal(cmd)
	fmt.Println("- With XML: ", string(buff))
}

actual output:

- With JSON:  {}
- With XML:  <Command><struct></struct></Command>

expected output:

- With JSON:  {}
- With XML:  <Command></Command>

openapi-generator version

openapitools/openapi-generator-cli:v7.2.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: mock
  version: 0.0.1
paths:
  /mock:
    post:
      operationId: post
      requestBody:
        content:
          application/xml:
            schema:
              $ref: '#/components/schemas/Command'
        required: true
      responses:
        '200':
          description: Successful response
          content:
            application/xml:
              schema:
                $ref: '#/components/schemas/Response'
components:
  schemas:
    Command:
      type: object
      properties:
        struct>member:
          type: array
          nullable: true
          description: List of Items
          items:
            $ref: "#/components/schemas/Item"
    Response:
      type: object
      properties:
        TYPE:
          type: string
          description: command
      required:
        - TYPE
    Item:
      type: object
      description: contains a member field
      properties:
        name:
          type: string
        value:
          type: string
      required:
        - name
        - value

Generation Details

> docker run --rm -it -v /test/tmp:/tmp -w /tmp openapitools/openapi-generator-cli:v7.2.0 generate -i /tmp/swagger.yaml --strict-spec true --additional-properties=useOneOfDiscriminatorLookup=true,withXml=true -p enumClassPrefix=true -g go -o /tmp/generated/model/ --package-name model --git-repo-id tmp/tmp/generated/model/

Steps to reproduce

0°) put the swagger.yaml into /test/tmp + mkdir -p generated/model
1°) run the generation command line from the
2°) run the provided go test

Linked Issues

• https://github.com/OpenAPITools/openapi-generator/pull/17594
• https://github.com/OpenAPITools/openapi-generator/issues/15891

Start with the provided swagger.yaml and generation command, then run the provided Go marshalling test to reproduce the generated Command output. Trace the Go generator's handling of nullable, non-required array properties with XML enabled; done when the generated field is *[]Item and empty XML omits struct>member while JSON remains omitted.