Using `allOf` and `nullable` in combination yields unexpected validation errors

What version of Ajv are you using? Does the issue happen if you use the latest version? I am using oas3-chow-chow which is using version ^6.12.3

Ajv options object oas3-chow-chow defines the AJV options as seen here.

const options: Ajv.Options = {
  /**
   * Ignore following formats for now because they are not supported by AJV by default.
   * TODO: Add custom format supports for following formats.
   */
  unknownFormats: [
    'int32',
    'int64',
    'float',
    'double',
    'byte',
    'binary',
    'password',
  ],
  nullable: true,
  jsonPointers: true,
};

export default function ajv(opts: Ajv.Options = {}) {
  return new Ajv({
    ...options,
    ...opts,
  });
}

JSON Schema Unfortunately I’m locked into using OAS 3.0.x and have to use the "nullable": true declaration

"MyArrayOfReferences": {
    "type": "array",
    "example": [
      "prefix/14691d5de8f424c75558dd7375",
      "prefix/6591827d39d443e983199e1cb7",
      "prefix/ec403e0c81074d8db34a6c9431"
    ],
    "items": { "type": "string" }
},
"UpdateMyArrayOfReferences": {
    "properties": {
        "myArrayOfReferences": {
          "description": "Group settings. Set to `null` to remove.",
          "allOf": [
            {
              "$ref": "#/components/schemas/MyArrayOfReferences"
            }
          ],
          "nullable": true
        }
    }
}

Sample data

{
    "myArrayOfReferences": null
}

Validation result, data AFTER validation, error messages

"dataPath": "/myArrayOfReferences",
"error message": "RequestValidationError: Schema validation error: type should be array",

What results did you expect? I expect to be able to provide a null value without producing a validation error.

It seems related to this issue #983 because if I remove the $ref and make everything inline, then the null value is accepted.

[crizo23]

Helping out @denver-HJS here.

Here is a runkit link: https://runkit.com/crizo23/611437b007a03a001a5b80e7 I couldn’t import AJV v6 though, so it won’t compile. I pasted the output I get on line 104

[epoberezkin]

I believe this is by design, “nullable” was defined as an extension of type keyword, not as an extension of the schema. If you have a schema that doesn’t allow null and you want to accept null you can just do:

{
  anyOf: [
    {$ref: "some_schema"},
    {const: null}
  ]
}

Below is not supposed to work:

{
  $ref: "some_schema",
  nullable: true
}