'ARRAY_ADDITIONAL_ITEMS' error unreachable?

[Ligengxin96]

If Array.isArray(json) is true, it means schema.type must be an Array.
So, schema.items always is an Object.
If i was wrong, how should I define a shcame to make this error reachable?

（JsonValidation.js line 108）

 additionalItems: function (report, schema, json) {
        // http://json-schema.org/latest/json-schema-validation.html#rfc.section.5.3.1.2
        if (shouldSkipValidate(this.validateOptions, ["ARRAY_ADDITIONAL_ITEMS"])) {
            return;
        }
        if (!Array.isArray(json)) {
            return;
        }
        // if the value of "additionalItems" is boolean value false and the value of "items" is an array,
        // the json is valid if its size is less than, or equal to, the size of "items".
        if (schema.additionalItems === false && Array.isArray(schema.items)) {
            if (json.length > schema.items.length) {
                report.addError("ARRAY_ADDITIONAL_ITEMS", null, null, schema);
            }
        }
    }