[PHP] nullable property not added to docblock typehint

Description

Properties on objects that are defined as nullable do not receive a nullable typehint in the docblock.

This is the code that is generated with a nullable property:

    /**
     * Gets activation_date
     *
     * @return \DateTime
     */
    public function getActivationDate()
    {
        return $this->container['activation_date'];
    }

But because it is nullable, it should add |null in the docblock:

    /**
     * Gets activation_date
     *
     * @return \DateTime|null
     */
    public function getActivationDate()
    {
        return $this->container['activation_date'];
    }

Because modern IDEs will check the typehint, there should be warnings about a property that might be nullable. Those warnings are never shown to the developers. As well as Static code analysis tools not being able to catch possible errors.

Swagger-codegen version

https://editor.swagger.io/ -> Online codegen: 3.0.20

Swagger declaration file content or url

openapi: 3.0.1
info:
  title: Some API
  version: 1.0.0
servers:
  - url: https://example.com/api
paths:
  /activations/users/{userId}:
    get:
      operationId: getActivationsForUser
      parameters:
        - name: userId
          in: path
          required: true
          schema:
            type: string
      responses:
        200:
          description: Retrieved activations for User
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ActivationsTO'
components:
  schemas:
    ActivationsTO:
      title: ActivationsTO
      type: object
      properties:
        activations:
          type: array
          items:
            $ref: '#/components/schemas/ActivationTO'
          nullable: true
      description: Object containing multiple ActivationTO
    ActivationTO:
      title: ActivationTO
      required:
        - id
      type: object
      properties:
        activationDate:
          type: string
          format: date-time
          nullable: true
        id:
          type: string
          format: uuid
          nullable: false
      description: Activation object

Command line used for generation

(Unknown, using online generator of https://editor.swagger.io/)

Steps to reproduce

Paste the above code into the editor and generate a PHP-Client.

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/pull/8162 does this for non-required parameters, but not for nullable parameters. But this PR is not merged as well

Suggest a fix/enhancement

Use the PR from above, but instead of using required use nullable

Start with PHP client generation from the supplied OpenAPI example and compare its nullable-property handling with pull request 8162. Done means generated PHP docblocks include |null for nullable properties such as activationDate and nullable arrays, while non-nullable properties remain unchanged.