swift-ring-builder /etc/swift/object.builder rebalance
Traceback (most recent call last):
  File "/usr/bin/swift-ring-builder", line 24, in <module>
    sys.exit(main())
  File "/usr/lib/python2.7/dist-packages/swift/cli/ringbuilder.py", line 866, in main
    Commands.__dict__.get(command, Commands.unknown.im_func)()
  File "/usr/lib/python2.7/dist-packages/swift/cli/ringbuilder.py", line 620, in rebalance
    parts, balance = builder.rebalance(seed=get_seed(3))
  File "/usr/lib/python2.7/dist-packages/swift/common/ring/builder.py", line 356, in rebalance
    self._reassign_parts(reassign_parts)
  File "/usr/lib/python2.7/dist-packages/swift/common/ring/builder.py", line 936, in _reassign_parts
    key=lambda t: (-other_replicas[t],
ValueError: max() arg is an empty sequence