Why is multiple types shown in a bad way in Swagger UI

I have the following open api schema:

    WaypointEntity:
      type: object
      properties:
        id:
          type: [number, "null"]

But it's not shown correctly in Swagger UI:

enter image description here

Any idea why that is? AmI specifying the types incorrectly? I'm using Open Api 3.0

Solution 1:

In OpenAPI 3.0, type cannot be a list of types, it must be a single type. A nullable number is defined like this:

id:
  type: number
  nullable: true   # <----

More info: How to define a property that can be string or null in OpenAPI?