issue with nullable fields

Hello

I use swagger to define APIS, their input and output parameters

In the case of Output parameters I define the following agregate in a domain :

schemas:
  account-token:
     type: object
     properties:
         k0:
          type: string
          nullable: true
        k1:
          type: string
         nullable: true
      status:
        type: string
       nullable: true

As you can see all 3 fields are nullable.

However the code generated by the code gen (for spring boot 2.1.7) ignores this property.

Furthermore evben if I add  this annotation

@Schema(nullable=true)

the nullable natude of those fields is ignored 

Is there something I do not do righ? Is it a bug?  

Can someone give me pointers?

Regards

Christsophe