code: private void assignMinimumTTL(List<? extends DnsAnswer> dnsAnswers, LookupResult.Builder builder) {
  
          if (config.hasOverrideTTL()) {
              builder.cacheTTL(config.getCacheTTLOverrideMillis());
          } else {
              // Deduce minimum TTL on all TXT records. A TTL will always be returned by DNS server.
              builder.cacheTTL(dnsAnswers.stream()
                                         .map(DnsAnswer::dnsTTL)
                                         .min(Comparator.comparing(Long::valueOf)).get() * 1000);
          }
      }
docs: Assigns the minimum TTL found in the supplied DnsAnswers. The minimum makes sense, because this is the least
  amount of time that at least one of the records is valid for.