class ActiveRecord::AssociationNotFoundError

def initialize(record = nil, association_name = nil)
  @record           = record
  @association_name = association_name
  if record && association_name
    super("Association named '#{association_name}' was not found on #{record.class.name}; perhaps you misspelled it?")
  else
    super("Association was not found.")
  end
end