Steps to reproduce the issue

1. Install Joomla 3.9 beta
2. Install the attached library
3. Then uninstall it

Expected result

The library is uninstalled

Actual result

Call to a member function attributes() on null
D:\www\beta\plugins\actionlog\joomla\joomla.php:428

Call stack

| Function | Location

1 | () | JROOT\plugins\actionlog\joomla\joomla.php:428
2 | PlgActionlogJoomla->onExtensionAfterUninstall() | JROOT\libraries\joomla\event\event.php:70
3 | JEvent->update() | JROOT\libraries\joomla\event\dispatcher.php:160
4 | JEventDispatcher->trigger() | JROOT\libraries\src\Installer\Installer.php:773
5 | Joomla\CMS\Installer\Installer->uninstall() | JROOT\administrator\components\com_installer\models\manage.php:246
6 | InstallerModelManage->remove() | JROOT\administrator\components\com_installer\controllers\manage.php:105
7 | InstallerControllerManage->remove() | JROOT\libraries\src\MVC\Controller\BaseController.php:710
8 | Joomla\CMS\MVC\Controller\BaseController->execute() | JROOT\administrator\components\com_installer\installer.php:19
9 | require_once() | JROOT\libraries\src\Component\ComponentHelper.php:382
10 | Joomla\CMS\Component\ComponentHelper::executeComponent() | JROOT\libraries\src\Component\ComponentHelper.php:357
11 | Joomla\CMS\Component\ComponentHelper::renderComponent() | JROOT\libraries\src\Application\AdministratorApplication.php:101
12 | Joomla\CMS\Application\AdministratorApplication->dispatch() | JROOT\libraries\src\Application\AdministratorApplication.php:159
13 | Joomla\CMS\Application\AdministratorApplication->doExecute() | JROOT\libraries\src\Application\CMSApplication.php:195
14 | Joomla\CMS\Application\CMSApplication->execute() | JROOT\administrator\index.php:51

lib_osphpexcel.zip

System information (as much as possible)

Joomla 3.9 beta

Additional comments

For some reasons, this command https://github.com/joomla/joomla-cms/blob/staging/plugins/actionlog/joomla/joomla.php#L425, $manifest is null and it causes the issue

Sometime, I also see that install library gets similar issue, too. Mean $manifest after this command is also null https://github.com/joomla/joomla-cms/blob/staging/plugins/actionlog/joomla/joomla.php#L368

The main question here is when install/uninstall extension, do we have a case which this command return null?
lib_osphpexcel.zip

$manifest      = $installer->get('manifest');