Deprecated: Creation of dynamic property Drupal\course\Storage\CourseObjectFulfillmentStorage::$entityClass is deprecated in /web/modules/contrib/course/src/Storage/CourseObjectFulfillmentStorage.php on line 40

Thanks @djdevin! The patch fixes an issue when progressing through Book and Quiz objects in a Drupal 10 course outline.

However, there are now some errors when editing a course outline:

1. After adding an object to the outline, a Drupal.AjaxError occurs. Reloading the page then shows the added object.
2. When deleting an object from the outline and then clicking 'Save outline', an exception is thrown:
   

   Call to a member function get() on null
   /src/Storage/CourseObjectFulfillmentStorage.php on line 106
   $ret = $available[$co->get('object_type')->getString()] ?? [];

   ** Note: I was running into this every time an object was deleted from the outline, but now I can't replicate (?).