[chef] NoMethodError: undefined method `[]' for nil:NilClass

[Stuart Cracraft < >]

I am getting this on chef-client of a node:

  FATAL: NoMethodError: undefined method `[]' for nil:NilClass. 

with this pointed out in relevant file content: 

  variables :vhost => node[:rabbitmq][:queue_name]

Any thoughts on what it means and how to approach it?