Re-using enums with YAML anchor causing com.fasterxml.jackson.databind.node.TextNode cannot be cast to com.fasterxml.jackson.databind.node.ArrayNode

Hi guys,

YAML anchors don't seem to be parsed correctly. I got the example from (https://github.com/swagger-api/swagger-editor/issues/609)

  swagger: '2.0'

  info:
    version: "0.0.1"
    title: API

  x-types:
    OperationType: &OperationType
      - registration

  paths:
    /checker:
      get:
        parameters:
          - name: operations
            in: query
            type: array
            items:
              type: string
              enum: *OperationType
            default: [registration]
        responses:
          200:
            description: OK
            schema:
              $ref: '#/definitions/OperationType'

  definitions:      
    OperationType:
      type: string
      enum: *OperationType

I tried to define the anchor in a different way - none of them works, giving me com.fasterxml.jackson.databind.node.TextNode cannot be cast to com.fasterxml.jackson.databind.node.ArrayNode

Reproduce the failure with the YAML example in the issue, focusing on the anchored enum used under parameters and definitions. Trace the OpenAPI parsing path that produces the Jackson TextNode-to-ArrayNode cast, then verify that the same document is accepted without that exception and that the enum remains usable in generated output.