type array list not validated in OAS 3.1

[adamaltman]

Describe the bug

When a schema has type null defined in YAML, it is being treated as a null value and not "null" the string that defines the types.

https://json-schema.org/understanding-json-schema/reference/null.html

https://github.com/Redocly/openapi-starter/blob/main/openapi/components/schemas/Schema.yaml#L41

I believe that Schema needs to be adjusted to the following to define the type properly:

  nullableOrStringProperty:
    description: Property name's description (type is string or null)
    type:
      - string
      - "null"

However, I then suspected that nothing in the type list is being validated:

Redocly/openapi-starter#74

This bug does not exist when type is defined as a string (for example the following would produce a problem):

type: foo

To Reproduce
Steps to reproduce the behavior:

1. See bug: reproduce a bad type openapi-starter#74
2. See error (that there is no problem)

Expected behavior

problem message:

type can be one of the following only: "object", "array", "string", "number", "integer", "boolean", "null".

Logs

There is no problem detected (which is the problem because there is a problem).

OpenAPI definition

OAS 3.1
https://github.com/Redocly/openapi-starter/blob/main/openapi/components/schemas/Schema.yaml#L41

Redocly Version(s)

1.0.0-beta.108

Node.js Version(s)

16.10

Additional context

• This was revealed by some crashing of our mock server.

[razvanphp]

Hmm, interesting, so my schema is invalid? null needs to always be defined as a string? Why?

allOf:
  - type: object
    properties:
      car:
        $ref: ./Car.yaml
      user:
        type:
          - object
          - null
        $ref: ./User.yaml
      user_id:
        type:
          - integer
          - null
      car_id:
        type:
          - integer
          - null

This was not triggering an error on 1.0.0-beta.125, but it does now.