On-demand evaluation not working

The "on-demand" evaluation feature does not seem to work. If the list of nodes to run self.nodes_torun is empty or None then the query is not specialized. It should be if self.nodes_torun is None then perform the original fw_query, if it is an empty list then it should simply return an empty list of fw_ids and not perform a query, otherwise it should extend the fw_query accordingly.