Nullable type should not appear in array of object type

[codeasashu]

steps to reproduce

1. Add a path
2. Add response, with object containing string key
3. try to make string key to nullable
4. See the resulting schema

Expected

responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                title: ''
                type: object
                properties:
                  status:
                    type: string
                    nullable: true

Actual

responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                title: ''
                type: object
                properties:
                  status:
                    type:
                          - string
                          - 'null'