Please help us help you and fill where relevant:
Your LimeSurvey version: 6.5.0
Own server or LimeSurvey hosting: on-prem inside IIS and MS SQL
Survey theme/template: Fruity Twenty Three
==================
Hi,

I upgraded to the latest version (6.4.12 previously and now 6.5.0) of limesurvey and I'm getting the error below

[error] [exception.TypeError] TypeError: array_key_exists(): Argument #2 ($array) must be of type array, null given in C:\inetpub\wwwroot\limesurvey\application\helpers\SurveyRuntimeHelper.php:389
Stack trace:
#0 C:\inetpub\wwwroot\limesurvey\application\controllers\survey\SurveyIndex.php(643): SurveyRuntimeHelper->run()
#1 C:\inetpub\wwwroot\limesurvey\application\controllers\survey\SurveyIndex.php(22): SurveyIndex->action()
#2 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\actions\CAction.php(76): SurveyIndex->run()
#3 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\CController.php(308): CAction->runWithParams()
#4 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\CController.php(286): CController->runAction()
#5 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\CController.php(265): CController->runActionWithFilters()
#6 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\CWebApplication.php(282): CController->run()
#7 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\web\CWebApplication.php(141): CWebApplication->runController()
#8 C:\inetpub\wwwroot\limesurvey\vendor\yiisoft\yii\framework\base\CApplication.php(185): CWebApplication->processRequest()
#9 C:\inetpub\wwwroot\limesurvey\index.php(161): CApplication->run()
#10 {main}

bugs.limesurvey.org/view.php?id=19478

github.com/LimeSurvey/LimeSurvey/commit/...ef2fd70ce6a1887e6d23