Missing protected static in TopicHandlerRegistry

  TopicHandlerRegistry.php extends Singleton but does not declare its own protected static $instance field. The Singleton base class explicitly requires this. Without it, the registry may share the parent's static instance with other Singleton subclasses, causing collisions.

Author: m1k3lm

src/BusinessLogic/ConfigurationWebhookAPI/Handlers/TopicHandlerRegistry.php

@@ -12,6 +12,11 @@
  */
 class TopicHandlerRegistry extends Singleton
 {
+    /**
+     * @var static
+     */
+    protected static $instance;
+
     /**
      * Map of registered topic handlers
      *