hammer supported-systems is broken

Hammer used to be able to print a list of supported systems. Sadly, it doesn't work for me anymore.

$ ./hammer.py supported-systems
fedora:
  - 2: 
  - 2: 
  - 2: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
  - 3: 
centos:
Traceback (most recent call last):
  File "/home/thomson/devel/kea/./hammer.py", line 3233, in <module>
    main()
  File "/home/thomson/devel/kea/./hammer.py", line 3190, in main
    list_supported_systems()
  File "/home/thomson/devel/kea/./hammer.py", line 2860, in list_supported_systems
    for r, supported in revisions_and_supported:
ValueError: not enough values to unpack (expected 2, got 1)

I used git bisect to find out which commit caused that. It seems it's cafead21.