code: public ClientFactoryBuilder addressResolverGroupFactory(
              Function<? super EventLoopGroup,
                       ? extends AddressResolverGroup<? extends InetSocketAddress>> addressResolverGroupFactory) {
          requireNonNull(addressResolverGroupFactory, "addressResolverGroupFactory");
          checkState(domainNameResolverCustomizers == null,
                     "addressResolverGroupFactory() and domainNameResolverCustomizer() are mutually exclusive.");
          this.addressResolverGroupFactory = addressResolverGroupFactory;
          return this;
      }
docs: Sets the factory that creates a {@link AddressResolverGroup} which resolves remote addresses into
  {@link InetSocketAddress}es.
  
  @throws IllegalStateException if {@link #domainNameResolverCustomizer(Consumer)} was called already.