Check for key existence to ensure compabilitity wit PHP 8

Classes/Controller/AbstractController.php

@@ -320,7 +320,7 @@ protected function sanitizeSettings(): void
  */
  protected function setDefaultIntSetting(string $setting, int $value): void
  {
- if (empty($this->settings[$setting])) {
+ if (!array_key_exists($setting, $this->settings) || empty($this->settings[$setting])) {
  $this->settings[$setting] = $value;
  } else {
  $this->settings[$setting] = (int) $this->settings[$setting];