WCF::handleException() Unhandled exception: Call to a member function canEnter() on null

#0 /home/filbboard/html_wbb4/lib/system/user/activity/event/PostUserActivityEvent.class.php(55): wbb\data\post\Post->canRead()
#1 /home/filbboard/html_wbb4/wcf/lib/data/user/activity/event/ViewableUserActivityEventList.class.php(82): wbb\system\user\activity\event\PostUserActivityEvent->prepare(Array)
#2 /home/filbboard/html_wbb4/wcf/lib/system/dashboard/box/RecentActivitySidebarDashboardBox.class.php(35): wcf\data\user\activity\event\ViewableUserActivityEventList->readObjects()
#3 /home/filbboard/html_wbb4/wcf/lib/system/dashboard/DashboardHandler.class.php(71): wcf\system\dashboard\box\RecentActivitySidebarDashboardBox->init(Object(wcf\data\dashboard\box\DashboardBox), Object(wbb\page\BoardListPage))
#4 /home/filbboard/html_wbb4/lib/page/BoardListPage.class.php(98): wcf\system\dashboard\DashboardHandler->loadBoxes('com.woltlab.wbb...', Object(wbb\page\BoardListPage))
#5 /home/filbboard/html_wbb4/wcf/lib/page/AbstractPage.class.php(276): wbb\page\BoardListPage->assignVariables()
#6 /home/filbboard/html_wbb4/wcf/lib/page/AbstractPage.class.php(100): wcf\page\AbstractPage->show()
#7 /home/filbboard/html_wbb4/wcf/lib/system/request/Request.class.php(58): wcf\page\AbstractPage->__run()
#8 /home/filbboard/html_wbb4/wcf/lib/system/request/RequestHandler.class.php(139): wcf\system\request\Request->execute()
#9 /home/filbboard/html_wbb4/index.php(10): wcf\system\request\RequestHandler->handle('wbb')
#10 {main}