Does not pick up default value if defined in $ref definition

[onury]

What version of Ajv are you using? Does the issue happen if you use the latest version? 4.8.2

Ajv options object (see https://github.com/epoberezkin/ajv#options):

{
    allErrors: true,
    format: 'full',
    useDefaults: true
}

JSON Schema (please make it as small as possible to reproduce the issue):

{
    ...
    "properties": {
        "phone": {
            "$ref": "#/definitions/optionalPhone"
        },
       ...
    },
    "definitions": {
        "emptyString": {
            "type": "string",
            "maxLength": 0
        },
        "optionalPhone": {
            "anyOf": [
                { "format": "phone" },
                { "$ref": "#/definitions/emptyString" }
            ],
            "default": ""
        }
    }
}

Above will work only if I define default: "" within phone.

Data (please make it as small as posssible to reproduce the issue):

{}

Validation result, data AFTER validation, error messages: Data after validation: {}
No errors. Just the default value is not set for phone.

What results did you expect? { phone: "" }