Version 2.8.0+ does not handle `@Schema(nullable = true)` fields correctly

[slovelo]

Describe the bug

• From springdoc 2.8.0 and newer, fields that are marked as nullable via @Schema(nullable = true) no longer show as nullable: true in the generated OpenAPI and swagger UI.
• This issue was introduced after 2.7.0. Tested with 2.8.5 and 2.8.0 which both exhibit the same bug.

To Reproduce
Steps to reproduce the behavior:

• Java 21, spring-boot 3.4.3
• springdoc-openapi-starter-webflux-ui 2.8.5
• Create a class and annotate all fields with @Schema(nullable = true)
• Expose this class via a get endpoint
• Inspect OpenAPI JSON or YAML. No fields will be nullable in OpenAPI spec

Sample OpenAPI YAML from 2.8.0 and 2.8.5

components:
  schemas:
    MyType:
      properties:
        id:
          format: int32
          type: integer

Expected behavior
Sample OpenAPI YAML from 2.7.0

components:
  schemas:
    MyType:
      properties:
        id:
          format: int32
          nullable: true
          type: integer

[slovelo]

Closing as OpenAPI 3.1 no longer supports nullable
See #2840 as others have commented