raise_on_circular_reference

# File activesupport/lib/active_support/json/encoding.rb, line 26
        def raise_on_circular_reference(value) #:nodoc:
          stack = Thread.current[REFERENCE_STACK_VARIABLE] ||= []
          raise CircularReferenceError, 'object references itself' if
            stack.include? value
          stack << value
          yield
        ensure
          stack.pop
        end