Open Api 3.0.3: nullable attribute

[drozenberg]

I'm using Open API v3.0.3 and I have a column that can be either a string or null. For example:

activated_at:
  type: string
  nullable: true
  format: date-time

When I do a fragment validation, however, I get the following error:

JSON::Schema::ValidationError: The property '#/activated_at' of type null did not match the following type: string

When I format my api doc according to the OpenApi v3.1 spec, it works. However, I can't use v3.1 for this particular project. The OpenApi v3.1 format is shown below:

activated_at:
  type:
     - string
     - 'null'

Is Open API v3.0.3 supported? Or is it validation done against 3.1 by default?

[ketiko]

I currently don't have a project using Open API 3 >=. So it hasn't been tested.