GetActorOfClass will return NULL when there are no actors of that class in the level.
Trying to access properties or call functions of a NULL pin will always log this kind of errors.
You can check the object is not null with an “Is Valid” check node.
Make sure you either added the EasyLevelDatabase actor in the level (just drag&drop in the map), or spawn it dynamically (from eg. gamemode class) with SpawnActor.