public function normalizeFKey($behavior)
    {
        if (null === $behavior) {
            return self::NONE;
        }

        $behavior = strtoupper($behavior);

        if ('NONE' === $behavior) {
            return self::NONE;
        }

        if ('SETNULL' === $behavior) {
            return self::SETNULL;
        }

        return $behavior;
    }