Your query is returning null because you are issuing query on a collection (video.movieDetails) which does not exist in the Atlas class cluster.
In order to be able to run this query, please connect to your Sandbox cluster.
The Class Atlas Cluster is owned by MongoDB and all the users have only Read Access to the databases in this cluster. You cannot perform Create, Update and Delete operation on the documents present in this cluster. This is so because we do not want any user to modify the contents of the databases and also to ensure every user has a consistent view of the data.
The Sandbox Atlas Cluster is created by each individual user such as you and you are the owner of this cluster with all the ReadandWrite access. In this cluster you load the video database and perform all sorts of CRUD operations.
If you still have any query, feel free to get back to us. Happy Learning
Curriculum Support Engineer