private function validateUnderlyingObjectType($object)
    {
        if (count($this->mustBeInstanceOf) == 0) {
            return true;
        }
        foreach ($this->mustBeInstanceOf as $instance) {
            if ($object instanceof $instance) { //|| $object->asa($instance) !== null
                return true;
            }
        }
        Yii::error('Got invalid underlying object type! (' . $object->className() . ')');
        return false;
    }