Context ParseError: syntax error, unexpected 'private' (T_PRIVATE), expecting end of file

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Hello There,

i have a problem in the nextcloud log which i dont really know how to solve.
It occured by outcomment the lines 150 to 155 in following app: guests/Mail.php at master · nextcloud/guests · GitHub

here its the log from the nextcloud backend:

[no app in context] Fatal: ParseError: syntax error, unexpected 'private' (T_PRIVATE), expecting end of file at <<closure>>

 0. /var/www/nextcloud/lib/composer/composer/ClassLoader.php line 428
    Composer\Autoload\includeFile()
 1. <<closure>>
    Composer\Autoload\ClassLoader->loadClass()
 2. <<closure>>
    spl_autoload_call()
 3. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 114
    ReflectionClass->__construct()
 4. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 133
    OC\AppFramework\Utility\SimpleContainer->resolve()
 5. /var/www/nextcloud/lib/private/AppFramework/DependencyInjection/DIContainer.php line 465
    OC\AppFramework\Utility\SimpleContainer->query()
 6. /var/www/nextcloud/lib/private/AppFramework/DependencyInjection/DIContainer.php line 437
    OC\AppFramework\DependencyInjection\DIContainer->queryNoFallback()
 7. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 89
    OC\AppFramework\DependencyInjection\DIContainer->query()
 8. <<closure>>
    OC\AppFramework\Utility\SimpleContainer->OC\AppFramework\Utility\{closure}("*** sensitive parameters replaced ***")
 9. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 108
    array_map()
10. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 116
    OC\AppFramework\Utility\SimpleContainer->buildClass()
11. /var/www/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php line 133
    OC\AppFramework\Utility\SimpleContainer->resolve()
12. /var/www/nextcloud/lib/private/AppFramework/DependencyInjection/DIContainer.php line 465
    OC\AppFramework\Utility\SimpleContainer->query()
13. /var/www/nextcloud/lib/private/AppFramework/DependencyInjection/DIContainer.php line 437
    OC\AppFramework\DependencyInjection\DIContainer->queryNoFallback()
14. /var/www/nextcloud/apps/guests/lib/AppInfo/Application.php line 69
    OC\AppFramework\DependencyInjection\DIContainer->query()
15. /var/www/nextcloud/apps/guests/lib/AppInfo/Application.php line 62
    OCA\Guests\AppInfo\Application->setupGuestManagement()
16. /var/www/nextcloud/lib/private/AppFramework/Bootstrap/Coordinator.php line 190
    OCA\Guests\AppInfo\Application->boot()
17. /var/www/nextcloud/lib/private/legacy/OC_App.php line 207
    OC\AppFramework\Bootstrap\Coordinator->bootApp()
18. /var/www/nextcloud/lib/private/legacy/OC_App.php line 140
    OC_App::loadApp()
19. /var/www/nextcloud/ocs/v1.php line 51
    OC_App::loadApps()
20. /var/www/nextcloud/ocs/v2.php line 23
    require_once("/var/www/nextcloud/ocs/v1.php")

Atfer i realized this error log i cancled the outcommenting.
I did a sudo reboot on my ubuntu system but this did not help.

can anyone help me to solve this error?

thank you!!