Steps to reproduce the issue

• Install nightly build Joomla_4.0.0-alpha5-dev-Development-Full_Package.zip 10 September 2018 02:

• Error reporting: Development (Global configuration)

• Go into Plugins > "System - Debug"

• Check first that plugin is enabled

• Deactivate everything but:
  "Refresh Assets" : YES (See issue #22121 why important).
  "Log Priorities" : ALL
  "Profiling" : SHOW
  "Log Executed Queries" : YES

• In another tab - Activate debug (Global configuration)

• Save plugin.

Expected result

• All fine and debug tabs below page

Actual result

White page with error:

Fatal error: 

Uncaught TypeError:
Argument 1 passed to Symfony\Component\Debug\ExceptionHandler::handle() must be an instance of Exception, instance of Error given in /libraries/vendor/symfony/debug/ExceptionHandler.php:106

Stack trace:
#0 [internal function]: Symfony\Component\Debug\ExceptionHandler->handle(Object(Error))
#1 {main}
  thrown in /libraries/vendor/symfony/debug/ExceptionHandler.php on line <b>106</b>

Additional comments

Only if both settings "Log Priorities" AND "Log Executed Queries" are enabled the error is thrown.

System information (as much as possible)

See System information in #22121 (comment)