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Easy question of the day: One of our headnodes is barking when I use
--fields with nova.

nova list --all --fields=host,instance_name,status
ERROR (TypeError): '<' not supported between instances of 'str' and 'NoneType'

This works fine with the other headnodes, and all 3 are supposed to be
the same (hardware, software). Would that indicate a bad installation
or something else? Where should I be looking for answers?