IC5 Beta 4 - Argument #1 ($output) must be of type array|string|null

Hi,

I'm using IC5 Beta4, and on my System Logs I have douzens of these errors, not quite sure what's causing them

TypeError: IPS\Lang::replaceWords(): Argument #1 ($output) must be of type array|string|null, stdClass given, called in /home/applications/forums/system/Lang/Lang.php on line 1811 (0)
#0 /home/applications/forums/system/Lang/Lang.php(1811): IPS\Lang->replaceWords(Object(stdClass))
#1 /home/applications/forums/system/Dispatcher/Api.php(378): IPS\Lang->parseOutputForDisplay(Object(stdClass))
#2 /home/applications/forums/api/index.php(11): IPS\Dispatcher\Api->run()
#3 {main}