message: [AMS] Make primaryVerificationKey nullable
diff: },
  "primaryVerificationKey": {
  "$ref": "#/definitions/ContentKeyPolicyRestrictionTokenKey",
  - "description": "The primary verification key."
  + "description": "The primary verification key.",
  + "x-nullable": true
  },
  "alternateVerificationKeys": {
  "type": "array",
  