[BUG] [Go] The omitEmpty json tag is not generated for oneOf fields.

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?

Actual:

type Variant struct {
	VariantA *VariantA
	VariantB *VariantB
}

Expected:

type Variant struct {
	VariantA *VariantA `json:"variantA,omitempty"`
	VariantB *VariantB `json:"variantB,omitempty"`
}

Description

The omitEmpty json tag is not generated for oneOf fields.

openapi-generator version

7.14.0

OpenAPI declaration file content

openapi: 3.0.0
info:
  title: Variant API
  version: 1.0.0
paths:
  /variant:
    get:
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Variant'
components:
  schemas:
    Variant:
      oneOf:
        - $ref: '#/components/schemas/VariantA'
        - $ref: '#/components/schemas/VariantB'

    VariantA:
      type: object
      properties:
        optionA:
          $ref: '#/components/schemas/OptionA'
      required:
        - optionA

    VariantB:
      type: object
      properties:
        optionB:
          $ref: '#/components/schemas/OptionB'
      required:
        - optionB

    OptionA:
      type: object
      properties:
        exampleField:
          type: string

    OptionB:
      type: object
      properties:
        exampleField:
          type: string

Generation Details

The command to generate the code:

docker run --rm \
  -v ${PWD}:/local \
  openapitools/openapi-generator-cli generate \
  -i /local/openapi.yaml \
  -g go \
  -o /local/out/go-client

Steps to reproduce

See 'Generation Details'

Related issues/PRs

n/a

Suggest a fix

n/a

Start by running the documented Docker generation command with the supplied openapi.yaml and inspect the generated Go Variant struct. Compare the oneOf fields with the expected output; done means the generated fields include the appropriate json tags with omitempty.