Steps to reproduce the issue

Clean installation from 3.9.12 to 4.0, put the menu module in the left position of Cassiopeia, open the frontend, log in, edit the menu module and change from right position to left position, the screen is blank with error message.

Expected result

Work usual

Actual result

{"error":true,"code":0,"message":"Call to a member function getType() on null"}

System information (as much as possible)

Mysql 5.7.27
Php 7.2.19

Additional comments

Enable debugger

{"error":true,"code":0,"message":"Call to a member function getType() on null","trace":"#0 /home/public_html/components/com_config/Controller/ModulesController.php(120): Joomla\Component\Modules\Administrator\Controller\ModuleController->save()\n#1 /home/public_html/libraries/src/MVC/Controller/BaseController.php(728): Joomla\Component\Config\Site\Controller\ModulesController->save()\n#2 /home/public_html/libraries/src/Dispatcher/ComponentDispatcher.php(146): Joomla\CMS\MVC\Controller\BaseController->execute('apply')\n#3 /home/public_html/libraries/src/Component/ComponentHelper.php(383): Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()\n#4 /home/public_html/libraries/src/Application/SiteApplication.php(205): Joomla\CMS\Component\ComponentHelper::renderComponent('com_config')\n#5 /home/public_html/libraries/src/Application/SiteApplication.php(244): Joomla\CMS\Application\SiteApplication->dispatch()\n#6 /home/public_html/libraries/src/Application/CMSApplication.php(241): Joomla\CMS\Application\SiteApplication->doExecute()\n#7 /home/public_html/includes/app.php(63): Joomla\CMS\Application\CMSApplication->execute()\n#8 /home/public_html/index.php(36): require_once('/home/pu...')\n#9 {main}"}