public static function getOneChildClass($parentClass)
    {
        $childClasses = self::getChildClasses($parentClass);

        /*
         * No child classes?
         * Oops, the base / parent class hasn't child class
         */
        if (empty($childClasses)) {
            throw MissingChildClassesException::create($parentClass);
        }

        /*
         * More than 1 child class?
         * Oops, the base / parent class has too many child classes
         */
        if (count($childClasses) > 1) {
            throw TooManyChildClassesException::create($parentClass, $childClasses);
        }

        return trim($childClasses[0]);
    }