Response schema marked as "Optional"

[Krismix1]

The response schema is marked as "Optional" but I don't think there is a way to mark it as required in the specification data (docs about describing responses in OA3).

Version: 0.6.4
Commit: 0beb11b
Reproduction spec:

openapi: 3.0.0
servers: []
info:
  description: |
    Example
  version: 1.0.0
  title: Swagger Petstore YAML
tags:
  - name: pet
    description: Everything about your Pets
paths:
  /pet:
    post:
      tags:
        - pet
      summary: Add a new pet to the store
      description: Add new pet to the store inventory.
      operationId: addPet
      responses:
        "200":
          description: successful operation
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Pet"
        "405":
          description: Invalid input
      requestBody:
        $ref: "#/components/requestBodies/Pet"
components:
  schemas:
    Pet:
      type: object
      required:
        - age
      properties:
        age:
          description: The age of the pet
          type: number
          example: 5
  requestBodies:
    Pet:
      content:
        application/json:
          schema:
            allOf:
              - description: My Pet
                title: Pettie
              - $ref: "#/components/schemas/Pet"
      description: Pet object that needs to be added to the store
      required: true