def default_timestamp_name(obj, next_state)
      at_name = "#{next_state}_at"
      on_name = "#{next_state}_on"
      case
      when obj.respond_to?(at_name) then at_name
      when obj.respond_to?(on_name) then on_name
      else
        fail NoMethodError, "Couldn't find a suitable timestamp field for event: #{@name}.
          Please define #{at_name} or #{on_name} in #{obj.class}"
      end
    end
def default_timestamp_name(obj, next_state)
      at_name = "#{next_state}_at"
      on_name = "#{next_state}_on"
      case
      when obj.respond_to?(at_name) then at_name
      when obj.respond_to?(on_name) then on_name
      else
        fail NoMethodError, "Couldn't find a suitable timestamp field for event: #{@name}.
          Please define #{at_name} or #{on_name} in #{obj.class}"
      end
    end
If @timestamp is true, try a default timestamp name