Marshaling schemas with additionalProperties back from openapi3.T has extra fields

[praneetloke]

An object with additionalProperties in the original open API doc that looks like this:

...
autoApprovers:
          type: object
          additionalProperties:
            type: array
            items:
              type: string
...

turns into this when a doc loaded from that is serialized back into YAML:

...
autoApprovers:
          type: object
          additionalProperties:
            has: null
            schema:
                type: array
                items:
                    type: string
...

Looks like kin-api needs a handler to marshal/unmarshal YAML similar to how it does with JSON. This causes validation of such schemas to fail because the has and the schema property under the additionalProperties object are treated as unknown "extras".

[praneetloke]

Should be fixed by getkin/kin-openapi#922.