I was joking. This is me, apparently.
Do you mean the path was empty? This is expected when you unmount any filesystem.
You can use the midclt command. Haven’t tried it myself, but it’s probably something like:
midclt call pool.dataset.lock mypool/mydataset
EDIT: You wouldn’t first unmount the dataset and then run that command. The above middleware command unmounts the filesystem and locks the dataset, as long as it is an “encryptionroot”. It’s the same thing as locking the dataset with the GUI.
I can only speak for TrueNAS Core, but I would think it’s the same for SCALE.
Just remember that if someone is currently using the SMB share, you won’t be able to unmount or lock the dataset.