TypeError: array_merge(): Argument #3 must be of type array, null given (0)

[Gregor21]

#0 /home/host400373/domains/xxx/public_html/system/Content/Content.php(2635): array_merge()
#1 /home/host400373/domains/xxx/public_html/system/Content/Item.php(1221): IPS\_Content->sendAfterEditNotifications()
#2 /home/host400373/domains/xxx/public_html/applications/forums/sources/Topic/Topic.php(678): IPS\Content\_Item->processAfterEdit()
#3 /home/host400373/domains/xxx/public_html/applications/forums/modules/front/forums/topic.php(678): IPS\forums\_Topic->processAfterEdit()
#4 /home/host400373/domains/xxx/public_html/system/Dispatcher/Controller.php(107): IPS\forums\modules\front\forums\_topic->edit()
#5 /home/host400373/domains/xxx/public_html/system/Content/Controller.php(50): IPS\Dispatcher\_Controller->execute()
#6 /home/host400373/domains/xxx/public_html/applications/forums/modules/front/forums/topic.php(39): IPS\Content\_Controller->execute()
#7 /home/host400373/domains/xxx/public_html/system/Dispatcher/Dispatcher.php(153): IPS\forums\modules\front\forums\_topic->execute()
#8 /home/host400373/domains/xxx/public_html/index.php(13): IPS\_Dispatcher->run()
#9 {main}

Hello, I am getting this error when adding a post/topic.

[Marc Stridgen]

Please disable all 3rd party items and then test this again. The issue you are having there, would tend to indicate an issue with items that arent compatible with PHP 8