Model validation incorrectly fails on responses with null fields

[jhendrixMSFT]

Regarding PR Azure/azure-rest-api-specs#2094.

{ code: 'RESPONSE_VALIDATION_ERROR',
  id: 'OAV108',
  message: 'Found errors in validating the response with statusCode "200" for x-ms-example "GetManagementGroup" in operation "ManagementGroups_Get".',
  innerErrors: 
   [ { code: 'INVALID_RESPONSE_BODY',
       errors: 
        [ { code: 'ONE_OF_MISSING',
            params: [],
            message: 'Data does not match any schemas from \'oneOf\'',
            path: [ 'properties' ],
            inner: 
             [ { code: 'ONE_OF_MISSING',
                 params: [],
                 message: 'Data does not match any schemas from \'oneOf\'',
                 path: [ 'properties', 'details' ],
                 inner: 
                  [ { code: 'ONE_OF_MULTIPLE',
                      params: [],
                      message: 'Data is valid against more than one schema from \'oneOf\'',
                      path: [ 'details', 'parent' ] },
                    { code: 'INVALID_TYPE',
                      params: [ 'null', 'object' ],
                      message: 'Expected type null but found type object',
                      path: [ 'details' ] } ] },
               { code: 'INVALID_TYPE',
                 params: [ 'null', 'object' ],
                 message: 'Expected type null but found type object',
                 path: [ 'properties' ] } ] } ],
       message: 'Invalid body: Data does not match any schemas from \'oneOf\'',
       path: [] } ] }

Here's the response.

    "responses": {
        "200": {
            "body": {
                "id": "/providers/Microsoft.Management/managementGroups/00000000-0000-0000-0000-000000000001",
                "type": "/providers/Microsoft.Management/managementGroups",
                "name": "00000000-0000-0000-0000-000000000001",
                "properties": {
                    "tenantId": "00000000-0000-0000-0000-000000000000",
                    "displayName": "Group Name 1",
                    "details": {
                        "version": 1,
                        "updatedTime": "2017-01-01T00:00:00.00Z",
                        "updatedBy": "Test",
                        "parent": null
                    }
                }
            }
        }
    }

Note the null parent field. How should this be modeled?
Seems related to #155

[amarzavery]

I was looking at this issue last night. This is a slightly complex problem to solve. Have sort of figured out the problematic part which has raised doubts in my mind about "oneOf". I need to improve my understanding of "oneOf" in json schema. Will have to talk to folks in the team and then come to a conclusion.

I would say please do not block on merging the PRs in the azure-rest-api-specs repo. We should definitely fix this issue in the upcoming sprint with more tests that have complicated scenarios.
/cc @salameer

[mcardosos]

Closing issue here as it is a linter issue, not model validator.

[amarzavery]

This StackOverflow link provides good explanation about requiredness type in a json document.