As per [json-schema specification](http://json-schema.org/latest/json-schema-validation.html#rfc.section.5.9): > if "items" is not present, or its value is an object, validation of the instance always succeeds, regardless of the value of "additionalItems"; Currently (v 4.0.x), CollectionConstraint makes an extra checks for "additionalItems" if "items" is object and fails validation