class ActiveSupport::Callbacks::Callback

def check_conditionals(conditionals)
  return EMPTY_ARRAY if conditionals.blank?
  conditionals = Array(conditionals)
  if conditionals.any?(String)
    raise ArgumentError, <<-MSG.squish
      Passing string to be evaluated in :if and :unless conditional
      options is not supported. Pass a symbol for an instance method,
      or a lambda, proc or block, instead.
    MSG
  end
  conditionals.freeze
end