code: public ClientFactoryBuilder domainNameResolverCustomizer(
              Consumer<? super DnsNameResolverBuilder> domainNameResolverCustomizer) {
          requireNonNull(domainNameResolverCustomizer, "domainNameResolverCustomizer");
          checkState(addressResolverGroupFactory == null,
                     "addressResolverGroupFactory() and domainNameResolverCustomizer() are mutually exclusive.");
          if (domainNameResolverCustomizers == null) {
              domainNameResolverCustomizers = new ArrayList<>();
          }
          domainNameResolverCustomizers.add(domainNameResolverCustomizer);
          return this;
      }
docs: Adds the specified {@link Consumer} which customizes the given {@link DnsNameResolverBuilder}.
  This method is useful when you want to change the behavior of the default domain name resolver, such as
  changing the DNS server list.
  
  @throws IllegalStateException if {@link #addressResolverGroupFactory(Function)} was called already.