public function getLoggedInUser($mapperName = \Tx_Oelib_Mapper_FrontEndUser::class)
    {
        if ($mapperName === '') {
            throw new \InvalidArgumentException('$mapperName must not be empty.', 1331488730);
        }
        if (!$this->isLoggedIn()) {
            return null;
        }

        if ($this->loggedInUser !== null) {
            $user = $this->loggedInUser;
        } else {
            /** @var \Tx_Oelib_Mapper_FrontEndUser $mapper */
            $mapper = \Tx_Oelib_MapperRegistry::get($mapperName);
            /** @var \Tx_Oelib_Model_FrontEndUser $user */
            $user = $mapper->find($this->getFrontEndController()->fe_user->user['uid']);
        }

        return $user;
    }