def catalog(opts = {})
      return nil unless catalog?

      opts[:replace] = true unless opts.key?(:replace)

      cat = Systemd::Journal.catalog_for(self[:message_id])
      # catalog_for does not do field substitution for us, so we do it here
      # if requested
      opts[:replace] ? field_substitute(cat) : cat
    end
def catalog(opts = {})
      return nil unless catalog?

      opts[:replace] = true unless opts.key?(:replace)

      cat = Systemd::Journal.catalog_for(self[:message_id])
      # catalog_for does not do field substitution for us, so we do it here
      # if requested
      opts[:replace] ? field_substitute(cat) : cat
    end
Returns the catalog message that this Journal Entry references, if any.
 @option opts [Boolean] :replace set to false to not replace placeholder
   strings in the catalog with the associated values in this Journal Entry.
   defaults to true.
 @return [String] the catalog provided message for this Journal Entry, or
   nil if non exists.