Best ActiveRecord error message ever

ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s)
:blocked_client_system or :blocked_client_systems in model GroupsBlkClientSystem.  Try 'has_many 
:blocked_client_systems, :through => :groups_blk_client_systems, :source => <name>'.
Is it one of :group or :client_system?

I was missing :source => :group from my association. Perfect message. The code knew what was missing, and it told me in a way that could be literally copied and pasted. Do write code like this when you can.