Use controller_name static config instead of method for better inheritance

code/Model/UserDefinedForm.php

@@ -29,8 +29,8 @@ class UserDefinedForm extends Page
      */
     private static $table_name = 'UserDefinedForm';
 
-    public function getControllerName()
-    {
-        return UserDefinedFormController::class;
-    }
+    /**
+     * @var string
+     */
+    private static $controller_name =  UserDefinedFormController::class;
 }