    def format_datetime(value, field_format)
      format = field_format || Blueprinter.configuration.datetime_format

      case format
      when NilClass then value
      when Proc then format.call(value)
      when String then value.strftime(format)
      else
        raise InvalidDateTimeFormatterError, 'Cannot format DateTime object with invalid formatter: #{format.class}'
      end
    end