docs: public static ImmutableSortedSet<String> hosts(String option) {
          checkArgument(option != null, "option is null");
          if (option.trim().isEmpty()) {
              return ImmutableSortedSet.of(
                      HostAndPort.fromParts("", Constants.DEFAULT_INTERNAL_PORT).toString());
          }
          Splitter commaSplitter = Splitter.on(',').omitEmptyStrings().trimResults();
          ImmutableSortedSet.Builder<String> sbld = ImmutableSortedSet.naturalOrder();
          for (String h: commaSplitter.split(option)) {
              checkArgument(isValidCoordinatorSpec(h), "%s is not a valid host spec", h);
              sbld.add(HostAndPort.fromString(h).withDefaultPort(Constants.DEFAULT_INTERNAL_PORT).toString());
          }
          return sbld.build();
      }