Depends on D19750. See T13210. The bin/drydock lease command makes it easier to request ad-hoc leases, but currently takes lease attributes in the form --attributes x=y,a=b.
This was okay for all leases at the time, but doesn't really work for modern WorkingCopy resources since they take a repositories.map which has a dictionary as a value. You can't specify that with repositories.map=....
Instead, point --attributes at a JSON file or use --attributes - to read from stdin.