How to "reset" a host's root password so that future deployments will use the root password from the hostgroup?

When deploying a host, I want the host to use the root password from the corresponding hostgroup. Some hosts have a local password set. I cannot figure out how to unset this. I tried setting host passwords to an empty string, like this:

hammer host update --root-password '' --name examplehost-$num

But that didn’t work. I ended up going directly to the database and running:

update hosts set root_pass = '' where hostgroup_id = 1;

That seems to work fine, but I’d prefer a way to do this that goes through the foreman api.