When creating hosts through the API with hammer, it's fairly unavoidable that you get a params hash containing:

"compute_attributes"=>{"volumes_attributes"=>{},"interfaces_attributes"=>{},"nics_attributes"=>{}}

due to hammer not knowing if a compute profile will be used or not via the host group.

set_compute_attributes in Host::Managed checks for compute_attributes.empty?, which will return false when these empty sub-hashes are present. It should be possible to use the compute profile even when passing in this empty data.

Either that, or CR VM creation should be reliable without them set to {}, but it currently isn't.