public function getLoggedInUser($mapperName = \Tx_Oelib_Mapper_BackEndUser::class)
    {
        if ($mapperName === '') {
            throw new \InvalidArgumentException('$mapperName must not be empty.', 1331318483);
        }
        if (!$this->isLoggedIn()) {
            return null;
        }
        if ($this->loggedInUser) {
            return $this->loggedInUser;
        }

        /** @var \Tx_Oelib_Mapper_BackEndUser $mapper */
        $mapper = \Tx_Oelib_MapperRegistry::get($mapperName);

        /** @var \Tx_Oelib_Model_BackEndUser $user */
        $user = $mapper->find($this->getBackEndUserAuthentication()->user['uid']);
        return $user;
    }