def include? date_time
      return false unless date_time.is_a?(String) || date_time.is_a?(DateTime)

      if date_time.is_a?(String)
        date_precision = Helper.determine_date_precision_of date_time
        date_time = Helper.date_time_from date_time, date_precision
      end

      result, = @data.bsearch { |d| d[0] >= date_time }
      result && result == date_time
    end
Check if a date exists in the index. Will be inferred from string in case
you pass a string. Recommened specifying the full date as a DateTime object.