--dumpDbUsersAndRoles flag dump the roles and users but it is empty

I am using this command to take a backup for myself on my local system but the users and roles collections are empty:

mongodump --uri mongodb+src://user:pass@sub.mongodb.net/db-name --dumpDbUsersAndRoles

And for restoring dumped data I run this command in terminal:

mongorestore --uri mongodb://user:pass@localhost:27017/db-name -d db-name /dump/db-name --restoreDbUsersAndRoles

and output is:

users file '/dump/db-name/$admin.system.users.bson' is empty; skipping users restoration
restoring users from /dump/db-name/$admin.system.users.bson
roles file '/dump/db-name/$admin.system.roles.bson' is empty; skipping roles restoration
restoring roles from /dump/db-name/$admin.system.roles.bson
1157176 document(s) restored successfully. 0 document(s) failed to restore.

What is wrong? Why it cannot dump the users and roles too?