I long for the day the CMS enforces proper property types instead of consistently passing invalid arguments all over the API...

Full error message:
Catchable fatal error: Argument 1 passed to Joomla\Utilities\ArrayHelper::toString() must be of the type array, string given, called in C:\wamp\www\develop\libraries\joomla\document\renderer\html\head.php on line 119 and defined in C:\wamp\www\develop\libraries\vendor\joomla\utilities\src\ArrayHelper.php on line 104

I also get:
Warning: Cannot modify header information - headers already sent by (output started at C:\wamp\www\develop\libraries\vendor\joomla\utilities\src\ArrayHelper.php:104) in C:\wamp\www\develop\libraries\kunena\error.php on line 264

Hi I had the same thing in VirtueMart 3.0.12 and in Kunena in my test with Joomla 3.5 beta 2
then I adjusted the head.php at line 114 thru 125 turn off
/libraries/joomla/document/renderer/html/head.php
maybe you can so continue with this solution that works for me

head.zip

on line 119

The fix has just merged, on the next version it will be there. or you can download the package on git, and overwrite the files.

closing this issue, since its merged.