check_conditionals

# File activesupport/lib/active_support/callbacks.rb, line 355
          def check_conditionals(conditionals)
            return EMPTY_ARRAY if conditionals.blank?

            conditionals = Array(conditionals)
            if conditionals.any? { |c| c.is_a?(String) }
              raise ArgumentError,                 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..squish
            end

            conditionals.freeze
          end