code: private static AuthoritativeNameServerList extractAuthoritativeNameServers(String questionName, DnsResponse res) {
          int authorityCount = res.count(DnsSection.AUTHORITY);
          if (authorityCount == 0) {
              return null;
          }
  
          AuthoritativeNameServerList serverNames = new AuthoritativeNameServerList(questionName);
          for (int i = 0; i < authorityCount; i++) {
              serverNames.add(res.recordAt(DnsSection.AUTHORITY, i));
          }
          return serverNames.isEmpty() ? null : serverNames;
      }
docs: Returns the {@code {@link AuthoritativeNameServerList} which were included in {@link DnsSection#AUTHORITY}
  or {@code null} if non are found.