Demo: required flag default value

Demo application reproducing the issue described here.

To run, execute the command below from project's root directory:

./gradlew clean generateOpenApiDocs

Then check generate documentation in openapi.yaml:

components:
  schemas:
    Resource:
#      required:                   # missing
#        - bar                     # 
#        - baz                     # 
#        - foo                     # 
      type: object
      properties:
        foo:
          type: string
        bar:
          type: boolean
        baz:
          type: object
      description: Resource schema