class ActiveRecord::HasManyThroughAssociationPolymorphicSourceError

def initialize(owner_class_name = nil, reflection = nil, source_reflection = nil)
  if owner_class_name && reflection && source_reflection
    super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}' without 'source_type'. Try adding 'source_type: \"#{reflection.name.to_s.classify}\"' to 'has_many :through' definition.")
  else
    super("Cannot have a has_many :through association.")
  end
end