[BUG] [kotlin-spring] allOf with single $ref loses sibling example in fromProperty #23335

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When a property uses allOf with a single $ref and has a sibling example, the generated code loses the example value. The @Schema annotation emits example = "null" (the literal string) instead of the actual example value from the spec.

This worked correctly in 6.x.

Actual output:

@Schema(example = "null", description = "Current status of the item.")
@get:JsonProperty("status") val status: StatusEnum? = null

The example becomes the literal string "null" instead of "ACTIVE".

Expected output:

@Schema(example = "ACTIVE", description = "Current status of the item.")
@get:JsonProperty("status") val status: StatusEnum? = null

openapi-generator version

Tested on 7.12.0 and 7.18.0. Worked correctly on 6.3.0.

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: Test API
  version: 1.0.0
paths:
  /test:
    get:
      operationId: getTest
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TestDTO'
components:
  schemas:
    TestDTO:
      type: object
      properties:
        status:
          description: Current status of the item.
          allOf:
            - $ref: '#/components/schemas/StatusEnum'
          example: ACTIVE
    StatusEnum:
      type: string
      enum: [ACTIVE, INACTIVE, PENDING]
      description: Status type.
      example: ACTIVE

Generation Details

openapi-generator-cli generate -i spec.yaml -g kotlin-spring -o output

Using kotlin-spring generator with interfaceOnly: true, useSpringBoot3: true.

Steps to reproduce

1. Generate code with the spec above using openapi-generator 7.12.0+
2. Check the generated TestDTO.kt

Related issues/PRs

• [BUG] allOf with single $ref element implementation doesn't respect sibling properties like deprecated etc. #17048 - same root cause, but only deprecated was fixed (PR Retain deprecated in allOf schema handling #17056)

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